Chapter 4: Metal Industry Emissions

CHAPTER 4

METAL INDUSTRY EMISSIONS

2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

4.1

Volume 3: Industrial Processes and Product Use

Authors
Section 4.2
Laura E. Dawidowski (Argentina), Oleksandra Kolmogortseva (Ukraine), Ingrid Person Rocha e Pinho (Brazil)
and Teruo Okazaki (Japan)

Section 4.4
Lukas Dion (Canada), Pernelle Nunez (IAI/UK), Alexey V. Spirin (Russian Federation) and David Sydney
Wong (New Zealand)

Section 4.8
David Sydney Wong (New Zealand), Lukas Dion (Canada), Pernelle Nunez (IAI/UK) and Alexey V. Spirin(Russian Federation).

Contributing Authors
Section 4.2
Jan Hendrik Reimink (WSA/Netherlands)

Section 4.4
Simon Gaboury (Canada), Jerry Y. Marks (USA), Andrey V. Panov (Russian Federation), Xin Bo (China) and
Xiping Chen (China).

Section 4.8
Michalopoulou Eleni (UK), Hanno Vogel (Germany), Youming Yang (China), Xin Bo (China) and Xiping Chen
(China).

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2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 4: Metal Industry Emissions

Contents
4

Metal Industry Emissions............................................................................................................................. 4.8
4.1

Introduction ........................................................................................................................................ 4.8

4.2

Iron & Steel and Metallurgical Coke Production ............................................................................... 4.9

4.2.1

Introduction .................................................................................................................................. 4.11

4.2.2

Methodological issues .................................................................................................................. 4.11

4.2.2.1

Choice of method: Metallurgical coke production – non fugitive emissions ...................... 4.12

4.2.2.2

Choice of method: iron and steel production ....................................................................... 4.17

4.2.2.3

Choice of emission factors .................................................................................................. 4.28

4.2.2.4

Choice of activity data ......................................................................................................... 4.31

4.2.2.5

Completeness....................................................................................................................... 4.32

4.2.2.6

Developing a consistent time series..................................................................................... 4.36

4.2.3

Uncertainty assessment ................................................................................................................ 4.36

4.2.4

Quality Assurance/Quality Control (QA/QC), Reporting and Documentation ............................ 4.36

4.3

Ferroalloy Production ....................................................................................................................... 4.37

4.4

Primary Aluminium Production ....................................................................................................... 4.38

4.4.1

Introduction to Primary Aluminium ............................................................................................. 4.39

4.4.2

Methodological issues for primary aluminium production .......................................................... 4.40

4.4.2.1

Choice of Method for CO2 emissions from primary aluminium production ....................... 4.40

4.4.2.2

Choice of emission factors for CO2 emissions from primary aluminium production .......... 4.40

4.4.2.3

Choice of method for PFCs ................................................................................................. 4.40

4.4.2.4

Choice of emission factors for PFCs ................................................................................... 4.53

4.4.2.5

Choice of activity data ......................................................................................................... 4.56

4.4.2.6

Completeness....................................................................................................................... 4.56

4.4.2.7

Developing a consistent time series..................................................................................... 4.57

4.4.3

Uncertainty assessment for primary aluminium production ......................................................... 4.59

4.4.3.1

Emission factor uncertainties............................................................................................... 4.59

4.4.3.2

Activity data uncertainties ................................................................................................... 4.61

4.4.4

Quality Assurance/Quality Control (QA/QC) Reporting and Documentation for primary aluminium
production..................................................................................................................................... 4.61

4.4.4.1

Quality Assurance/Quality Control (QA/QC) ..................................................................... 4.61

4.4.4.2

Reporting and documentation .............................................................................................. 4.62

4.4.5

Methodological issues for alumina production ............................................................................ 4.64

4.4.5.1

Alternative alumina refining processes ............................................................................... 4.64

4.4.5.2

Choice of method for alumina production ........................................................................... 4.67

4.4.5.3

Choice of emission factors for alumina production ............................................................. 4.74

4.4.5.4

Choice of activity data ......................................................................................................... 4.75

4.4.5.5

Completeness....................................................................................................................... 4.76

4.4.5.6

Developing a consistent time series..................................................................................... 4.77

4.4.6

Uncertainty assessment for alumina production........................................................................... 4.77

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Volume 3: Industrial Processes and Product Use

4.4.6.1

Emission factor uncertainties............................................................................................... 4.77

4.4.6.2

Activity data uncertainties ................................................................................................... 4.77

4.4.7

Quality Assurance/Quality Control (QA/QC), Reporting and Documentation for alumina
production..................................................................................................................................... 4.79

4.4.7.1

Quality Assurance / Quality Control (QA/QC) ................................................................... 4.79

4.4.7.2

Reporting and Documentation ............................................................................................. 4.80

4.5

Magnesium Production ..................................................................................................................... 4.81

4.6

Lead Production................................................................................................................................ 4.81

4.7

Zinc Production ................................................................................................................................ 4.81

4.8

Rare Earths Production ..................................................................................................................... 4.82

4.8.1

Introduction .................................................................................................................................. 4.82

4.8.2

Methodological Issues .................................................................................................................. 4.83

4.8.2.1

Choice of method for CO2 emissions from primary rare earth metal production ................ 4.83

4.8.2.2

Choice of emission factors for CO2 emissions from primary rare earth metal production .. 4.86

4.8.2.3

Choice of method for PFCs ................................................................................................. 4.87

4.8.2.4

Choice of emission factors for PFCs ................................................................................... 4.91

4.8.2.5

Choice of activity data and emission factors ....................................................................... 4.92

4.8.2.6

Completeness....................................................................................................................... 4.92

4.8.2.7

Developing a consistent time series..................................................................................... 4.93

4.8.3

Uncertainty assessment ................................................................................................................ 4.93

4.8.3.1

Emission factor uncertainties............................................................................................... 4.93

4.8.3.2

Activity data uncertainties ................................................................................................... 4.94

4.8.4

Quality Assurance/Quality Control (QA/QC), Reporting and Documentation ............................ 4.94

4.8.4.1

Quality Assurance/Quality Control (QA/QC) ..................................................................... 4.94

4.8.4.2

Reporting and Documentation ............................................................................................. 4.95

References ...................................................................................................................................................... 4.96

Equations
Equation 4.1 (Updated) CO2 emissions from Coke production (Tier 1a) ........................................................ 4.15
Equation 4.1a (New)CH4 emissions from Coke production (Tier 1a) ........................................................ 4.15

Equation 4.1b (New)CO2 emissions from metallurgical coke production (Tier 1b) ................................... 4.15

Equation 4.2 (Updated) CO2 emissions from metallurgical coke production .................................................. 4.16
Equation 4.4

CO2 emissions from iron and steel production (Tier 1) ............................................. 4.23

Equation 4.5

CO2 emissions from production of pig iron not processed into steel (Tier 1) ........... 4.23

Equation 4.6

CO2 emissions from production of direct reduced iron (Tier 1) ................................ 4.23

Equation 4.7

CO2 emissions from sinter production (Tier 1) ......................................................... 4.23

Equation 4.8

CO2 emissions from pellet production (Tier 1) ......................................................... 4.23

Equation 4.8a (New)CO2 emissions from BFG and LDG flaring (Tier 1) ................................................. 4.23

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Chapter 4: Metal Industry Emissions

Equation 4.9 (Updated) CO2 emissions from iron and steel production (Tier 2) ............................................. 4.24
Equation 4.10 (Updated) CO2 emissions from sinter production (Tier 2) ......................................................... 4.24
Equation 4.11

CO2 emissions from direct reduced iron production (Tier 2) .................................... 4.25

Equation 4.12

CH4 emissions from sinter production (Tier 1) ......................................................... 4.26

Equation 4.13

CH4 emissions from blast furnace production of pig iron (Tier 1) ............................ 4.26

Equation 4.14

CH4 emissions from direct reduced iron production (Tier 1) .................................... 4.27

Equation 4.14a (New)N2O emissions from flaring (Tier 1) .......................................................................... 4.27

Equation 4.24a (New)

Total PFC emissions .................................................................................................. 4.42

Equation 4.25 (Updated) HVAE PFC emissions (Tier 1 method) ..................................................................... 4.46
Equation 4.26 (Updated) HVAE PFC emissions by Slope method (Tier 2a and Tier 3a methods) ................... 4.46
Equation 4.27 (Updated) HVAE PFC emissions by Overvoltage method (Tier 3a method) ............................. 4.47
Equation 4.27a (New)HVAE PFC emissions (Tier 2b and Tier 3b method – (Marks & Nunez 2018a)) ..... 4.48

Equation 4.27b (New)HVAE PFC emissions (Tier 2b and Tier 3b method – (Dion et al. 2018a) )............. 4.49

Equation 4.27c (New)

LVAE PFC emissions (Tier 1 and Tier 3 methods – production-based) ................... 4.50

Equation 4.27d (New)

LVAE PFC emissions (Tier 3 method – as ratio of HVAE emissions) ..................... 4.50

Equation 4.27e (New)

Total PFC emissions for start-up of electrolysis cells (Tier 3csu method) .................. 4.51

Equation 4.27f (New)

Emission rate coefficients for HVAE PFC (Tier 2b method – (Dion et al. 2018a)) .. 4.55

Equation 4.27g (New)

Tier 1: Sintering process emissions based on alumina production data..................... 4.68

Equation 4.27h (New)

Tier 3: Emissions based on carbonate raw material inputs to the sintering kiln ........ 4.71

Equation 4.27i (New)

Emissions captured during Carbonisation process and contained in produced sodium
carbonate ................................................................................................................... 4.72

Equation 4.27j (New)

Emissions from un-calcined SKD not recycled to the kiln ........................................ 4.73

Equation 4.27k (New)Weighted average content CO2 in ‘i’ Bauxite (Nepheline) ore ................................ 4.73

Equation 4.27l (New)

Potential Emissions from Bauxites (Nephelines) residue .......................................... 4.73

Equation 4.27m (New)

Emissions from carbon-bearing non-fuel materials ................................................... 4.73

Equation 4.27n (New)CO2 absorption through use of circulating water collected from bauxite/nepheline
storage residue area and/or absorption through bauxite residue neutralization ......... 4.74

Equation 4.35 (New)Process CO2 Emissions from anode consumption (Tier 1) ........................................ 4.85

Equation 4.36 (New)Process CO2 Emissions from anode consumption (Tier 3) ........................................ 4.85

Equation 4.37 (New)PFC emissions from rare earth metals production (Tier 1 and Tier 3) ...................... 4.90

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Volume 3: Industrial Processes and Product Use

FiguresFigure 4.1

Illustration of main processes for integrated iron and steel production ..................... 4.10

Figure 4.6 (Updated)

Estimation of CO2 emissions from metallurgical coke production............................ 4.17

Figure 4.7 (Updated)

Decision tree for estimation of CO2 emissions from iron and steel production......... 4.19

Figure 4.8a (New)

Decision tree for estimation of CH4 emissions from coke production....................... 4.20

Figure 4.8b (Updated)

Decision tree for estimation of CH4 emissions from iron and steel production .......... 4.21

Figure 4.8c (New)

Decision tree for estimation of N2O emissions from iron and steel production.......... 4.22

Figure 4.8d (New)

Energy or IPPU CO2 emissions allocation in an integrated iron and steel facility ..... 4.34

Figure 4.12 (Updated)

Decision tree for calculation of HVAE related PFC emissions from primary aluminium
production ................................................................................................................... 4.43

Figure 4.12a (New)

Decision tree for calculation of LVAE related PFC emissions from primary aluminium
production ................................................................................................................... 4.44

Figure 4.12b (New)

Alumina production processes .................................................................................... 4.65

Figure 4.12c (New)

Decision tree for estimation of CO2 emissions from alumina production .................. 4.70

Figure 4.17 (New)

Decision tree for calculation of CO2 emissions from primary rare earth (RE) metal
production ................................................................................................................... 4.84

Figure 4.18 (New)

Decision tree for calculation of PFC emissions from primary rare earth (RE) metal
production ................................................................................................................... 4.89

TablesTable 4.1a (New)

Emission allocation from metallurgical coke production ........................................... 4.12

Table 4.1b (New)

Tiers to estimate CO2 emissions from metallurgical coke production – Non fugitive
emissions .................................................................................................................... 4.14

Table 4.1 (Updated)

Tier 1 default CO2 emission factors for coke production ........................................... 4.28

Table 4.1a (New)

Tier 1 default CO2 emission factors for sinter and pellet production.......................... 4.29

Table 4.1b (New)

Tier 1 default CO2 emission factors for iron and steel production ............................. 4.29

Table 4.2 (Updated)

Tier 1 default CH4 emission factors for coke production (non fugitives), iron and steel
production ................................................................................................................... 4.30

Table 4.2b (New)

Tier 1 default N2O emission factors for coke production and iron and steel production.................................................................................................................................... 4.30

Table 4.3 (Updated)

Tier 2 material-specific carbon contents for iron and steel production (tonnes C/tonne).................................................................................................................................... 4.31

Table 4.4 (Updated)

Uncertainty ranges ...................................................................................................... 4.36

Table 4.14a (New)

Summary of accounting methods for PFC emissions ................................................. 4.45

Table 4.15 (Updated)

Technology specific default emission factors for the calculation of HVAE and LVAE
emissions from aluminium production (Tier 1 method) (Marks & Nunez 2018b) ..... 4.53

Table 4.16 (Updated)

Technology specific coefficients for the calculation of HVAE PFC emissions fromaluminium production using slope methodology (Tier 2a method) (Marks & Nunez
2018b) ......................................................................................................................... 4.54

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Chapter 4: Metal Industry Emissions

Table 4.16a (New)Specific HVAE-CF4 emission rate coefficients based on the anode effect duration as
calculated by (Marks & Nunez 2018a) (Tier 2b method). .......................................... 4.54

Table 4.16b (New)

Uncertainty range (%) in estimating PFC emissions from individual HVAEs (Tier 2b
methods) ..................................................................................................................... 4.55

Table 4.16c (New)Time period of measurements used to establish updated Tier 1 default EFs and Tier 2adefault slope coefficients ............................................................................................ 4.58

Table 4.16d (New)

Summary of which guidelines to refer to, for time consistent PFC inventories ......... 4.59

Table 4.17 (Updated)

Good practice reporting information for calculating CO2 and PFC emissions fromaluminium production by tier ..................................................................................... 4.63

Table 4.17a (New)Technology specific default emission factors for the calculation of CO2 emissions fromalternative sintering processes (Tier 1 method) .......................................................... 4.74

Table 4.17b (New)

Default uncertainty values for Bauxite/nepheline sintering processes........................ 4.78

Table 4.26 (New)

Tier 1 default emission factors for calculating CO2 emissions from anode consumption.................................................................................................................................... 4.86

Table 4.27 (New)Data sources and uncertainties for parameters used in Tier 3 method for CO2 emissions
from anode consumption ............................................................................................ 4.87

Table 4.28 (New)

Tier 1 default emission factors and uncertainty ranges for the calculation of PFC
emissions from rare earth production ......................................................................... 4.91

Table 4.29 (New)Data sources and uncertainties for parameters used in Tier 3 method for PFC emissions.................................................................................................................................... 4.92

Table 4.30 (New)Good practice reporting information for calculating CO2 and PFC emissions from rareearth metal production by Tier.................................................................................... 4.95

Boxes
Box 4.0 (New)

Flaring activities in metallurgical coke and iron and steel productions ...................... 4.13

Box 4.1a (New)Fully automated anode effect intervention strategies for PFC emissions ................... 4.40

Box 4.2 (Updated)

High and low voltage anode effect description........................................................... 4.41

Box 4.3 (New)PFC emissions during start-up of electrolysis cells .................................................... 4.51

Box 4.4 (New)Anode effect description (for rare earth metal production by fluoride electrolysis) ... 4.88

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Volume 3: Industrial Processes and Product Use

4 METAL INDUSTRY EMISSIONS
Users are expected to go to Mapping Tables in Annex 5, before reading this chapter. This is required to correctly
understand both the refinements made and how the elements in this chapter relate to the corresponding chapter
in the 2006 IPCC Guidelines.

4.1

INTRODUCTION

No refinement.

4.8

2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 4: Metal Industry Emissions

4.2

IRON & STEEL AND METALLURGICAL COKE
PRODUCTION

The production of iron and steel leads to emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide(N2O). This chapter provides guidance for estimating emissions of CO2 and CH4. 1
The iron and steel industry broadly consists of:•Primary facilities that produce both iron and steel;•

Secondary steelmaking facilities;•

Iron production facilities; and•Offsite production of metallurgical coke.

Figure 4.1 illustrates the main processes for iron and steel production: metallurgical coke production, sinterproduction, pellet production, iron ore processing, iron making, steelmaking, steel casting and very often
combustion of blast furnace and coke oven gases for other purposes. The main processes may occur under what
is referred to as an ‘integrated’ facility and typically include blast furnaces, and basic oxygen steelmaking furnaces(BOFs), or in some cases open hearth furnaces (OHFs). It is also common for parts of the production to be offsite
under the responsibility of another operator such as an offsite coke production facility.
In some countries, there will be coke production facilities that are not integrated with iron and steel production(i.e., ‘offsite’). This chapter provides guidance for estimating emissions of CO2 and CH4 from all coke production
to ensure consistency and completeness. Countries should estimate emissions from onsite and offsite cokeproduction separately under higher tiers as the by-products of onsite coke production (e.g., coke oven gas, cokebreeze, etc.) are often used during the production of iron and steel.
Primary and secondary steel-making:Steel production can occur at integrated facilities from iron ore, or at secondary facilities, which produce steel
mainly from recycled steel scrap. Integrated facilities typically include coke production, blast furnaces, and BOFs,
or in some cases OHFs. Raw steel is produced using a basic oxygen furnace from pig iron produced by the blast
furnace and then processed into finished steel products. Pig iron may also be processed directly into iron products.
Secondary steelmaking most often occurs in electric arc furnaces (EAFs). In 2003, BOFs accounted forapproximately 63 percent of world steel production and EAFs approximately accounted for 33 percent; OHF
production accounted for the remaining 4 percent but is today declining.

Iron production:
Iron production can occur onsite at integrated facilities or at separate offsite facilities containing blast furnaces and
BOFs. In addition to iron production via blast furnace, iron can be produced through a direct reduction process.
Direct reduction involves the reduction of iron ore to metallic iron in the solid state at process temperatures lessthan 1000°C.

Metallurgical coke production:
Metallurgical coke production is considered to be an energy transformation of fossil fuel, and as a result the
combustion and fugitive emissions from coke production should be reported in the Energy Sector. Methodologies
for emissions from the combustion of fuels in coke production are included in the Energy volume, section 2.3,
whilst the methodologies for fugitive emissions (including emissions from flaring of Coke Oven Gas(CGO)) are
included in the Energy sector, section 4.3. Combustion emissions from coke production are reported in 1A1ci (seeVolume 2: Energy, table 2.1), whilst fugitive (including flaring) emissions are reported in 1B1cii (see Volume 2:
Energy, table 4.3.4).
Emission estimation methodologies for coke production are presented here in Volume 3, however, because theactivity data used to estimate emissions from energy and non-energy in integrated iron and steel production havesignificant overlap.

1

No methodologies are provided for N2O emissions. These emissions are likely to be small, but countries can calculate
estimates provided they develop country-specific methods based on researched data.

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Volume 3: Industrial Processes and Product Use

Figure 4.1

Illustration of main processes for integrated iron and steel production*
CokingCoal

Coke Oven Gas

Coke Plant

Coke
BreezeSinter Plant
Iron Ore.
Additives

Iron Ore.
Additives

Basic Oxygen
Furnace Gas

Pelletizing
Plant
Steelmaking[Basic Oxygen
Furnace]

Blast furnace
pig ironproduction

Steel
to
Steel Processing

Coal
Injection

Pig IrontoIron Processing

Modifiedconference
from: European
Conference
on "TheASevilla
A Driver for
Environmental
Performancein Industry"
6 and
7 April2000,
BREF onIron and Steel*Modified from:*European
on “TheSevilla Process:DriverProcess:for Environmental
Performancein Industry”
Stuttgart,
6 and 7 Stuttgart,
April 2000,
BREF
on theProduction
ofthe
IronProductionand Steel –ofconclusion
on BAT,
Dr.Haraldconclusion
onGovernmental
BAT, Dr. Harald
Schoenberger,
Regional
Governmental
Office Freiburg, April 2000. (Schoenberger, 2000)
Schoenberger, Regional
State
OfficeFreiburg, April
2000.State(Schoenberger,
2000)

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Chapter 4: Metal Industry Emissions

4.2.1

Introduction

No refinement.

4.2.2

Methodological issues

Inventory compilers should ensure that all emissions from coke production are included in their inventories but
are not double-counted. The section below highlights methodological options and indicates good practice in termsof reporting allocations, noting that methodologies are also presented in the Energy sector for combustion
emissions (Volume 2: Energy, section 2.1) and fugitive emissions (Volume 2: Energy, section 4.3) from cokeproduction.
The coke-making process comprises: (1) coal handling and preparation, including transportation, discharge,
storage, crushing, bed blending, that in all cases cause dust emissions, but not GHG emissions, and other following
stages where GHG emissions do occur, which are (2) coke oven battery operations, including coal charging,chamber heating and firing , coking, coke pushing and quenching and coke handling (i.e. storing, transporting,crushing and screening), and (3) coke oven gas treatment. The term ‘coking’ refers to the Carbonisation processthat takes place in the ovens which is a thermal distillation process that removes volatile matter from the coking
coal, in the form of gases or liquids, to produce coke. There are two technological options for coke-making which
differ primarily in the treatment of coke-making by-products:•

Coke production with by-product recovery where organic liquids, including coal tar and light oil, arerecovered;•Coke production without by-product recovery, where all ovens operate under negative pressure and,
consequently, there are no leakages under normal operating conditions. All the by-products are retained
and burned, instead of recovered. This process is usually accompanied by heat recovery and, in manycases, also the cogeneration of electricity.

GHG emission sources from metallurgical coke production include:•

Stack emissions which comprise GHG emissions from both the carbonisation (fuel transformation) of thecoal, and from fuel combustion. These emissions should all be reported in the Energy Sector, in
Manufacture of Solid Fuels in IPCC category 1.A.1.c. The emission estimation methodology from thecarbonisation of coal, including emissions from fuel combustion to heat the coke ovens, is presented here
as there is a significant overlap with the activity data used for iron and steel production. The Energy
Volume (Chapter 2 Volume 2 of 2006 IPCC Guidelines) also presents an estimation methodology for
combustion emissions is described in Chapter 2 Volume 2 of 2006 IPCC Guidelines that may be applied
to the activity data of fuel use to heat the coke ovens; therefore, care must be taken not to duplicate theemission estimates from fuel use in coke manufacture, within Energy and Industrial Processes andProduct Use (IPPU).

•

Fugitive emissions, which comprise:oDiffuse emissions (i.e. not emitted via stacks or vents) that occur during regular or irregular operations,originating from the transportation of coke, the use of ascension pipes, coke pushing, quenching andleakages in the battery. These diffuse emission sources are inherently difficult to monitor and therefore
to quantify. CH4 is the only GHG with significant diffuse emissions. These emissions should bereported under the Energy Sector, in the Fugitive emissions subsection (IPCC category 1.B.1c), and themethodology to estimate them is presented in Chapter 4 Volume 2 of the 2019 Refinement.

oFlaring emissions of, inter alia, CO2, CH4 and N2O which occur primarily during emergencies and COG
consumer maintenance. Where coke production is integrated with iron and steel manufacturing
facilities, COG is usually burned as part of a gas mixture that contains blast furnace gas (BFG) andother gases produced, such as converter gas. Where these gases are used for the coke production, theseemissions should be reported under the Energy Sector: (1) CH4 and N2O in IPCC category 1.B.1c , andthe methodology to estimate them is presented Section 4.3.2.2 Chapter 4 Volume 2 of the 2019
Refinement, and (2) CO2 should also be reported under IPCC 1.B.1c category, except for when thesimplified mass-balance approach is applied (Tier 1.b) and in that instance the CO2 emissions should
be reported together with direct emissions under the category 1.A.1.c. (Refer to Box 4.0) .

oVenting emissions of un-burned COG rarely occur and are considered negligible.

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Table 4.1a presents a summary of the allocation of emissions from metallurgical coke production.
TABLE 4.1A (NEW)EMISSION ALLOCATION FROM METALLURGICAL COKE PRODUCTION
Processes and gases
Coal charging

Chamber heating andfiringCokingCoke pushing

Coke quenching

Emergencies and
COG consumer
maintenance among
other reasons

Carbonisation
emissionsCombustion
emissions

Fugitive emissions
Diffuse emissions

Flaring emissions

CO2

NO

NO

NO

NO

CH4

NO

NO

1.B.1c (3)

NO

N2O

NO

NO

NO

NO

CO2

NO

1.A.1.c (2)

NS

NO

CH4

NO

1.B.1c (3)

NO

N2O

NO

NO

NO

CO2

1.A.1.c (1)

NS

NO

CH4

1.B.1c (3)

NO

N2O

NO

NO

NO

CO2

NO

NO

NS

NO

CH4

NO

NO

1.B.1c (3)

NO

N2O

NO

NO

NO

NO

CO2

NO

NO

NS

NO

CH4

1.A.1.c (1)NO

1.B.1c (3)

NO

N2O

NO

NO

NO

NO

CO2

NO

NO

NS

1.B.1c (3)and
1.A.1.c (1) (4)

CH4

NO

NO

1.B.1c (3)1.B.1c

N2O

NO

NO

NS

Note:
NS: Not significant, NO: not occurring(1)

Methodology described in this chapter(2)

Methodology described in Chapter 2, Volume 2 of 2006 IPCC Guidelines(3)

Methodology described in Chapter 4 Volume 2 of the 2019 Refinement(4)

When simplified carbon balance approach is used (Tier 1.b)4.2.2.1

C HOICE OF METHOD : M ETALLURGICAL COKE
PRODUCTION – NON FUGITIVE EMISSIONSThis section outlines three Tiers for calculating CO2 and CH4 emissions from metallurgical coke production. In allcases, the methods encompass emissions from carbonisation and fuel combustion.
The Tier used to estimate emissions will depend on the quantity and quality of data that is available for national
inventory compilers. The decision tree in Figure 4.6 will help select the Tier to be used to estimate CO2 emissions.
For CH4 emissions, the decision tree is presented in Figure 4.8a.
There are two Tier 1 method options to estimate CO2 emissions, depending on the activity data that are available:•

4.12

Tier 1 a: Where only metallurgical coke production data are available, the methodology applies a default
emission factor given in Table 4.1, corresponding to the type of coke production technology. Thismethodology takes into consideration default emission factors derived from stack measurements,
comprising the emissions from carbonisation (fuel transformation) and combustion, reflecting that there
is no practical way to measure the two parameters separately. Where this method is applied, the2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 4: Metal Industry Emissions

corresponding CO2 fugitive emissions from flaring should be estimated according to the methodology
described in Section 4.3.2.2 Chapter 4 Volume 2 of the 2019 Refinement (category 1.B.1c).
•

Tier 1 b: Where, in addition to data on metallurgical coke production, the country also has data on the
consumption of metallurgical coal, then it is good practice to use the simplified carbon mass balance
approach, assuming that all coke oven gas is combusted for coke production. This simple carbon balancemethod encompasses all carbon that may be released via fugitive emissions (including unintended
releases, flaring) and from the consumption of coke oven by-products. In most countries with cokeproduction, the required activity data for this method are readily available from national statistics and/or
operators, and as this method is associated with lower uncertainty than the Tier 1a approach, it is thepreferred Tier 1 method where the activity data are available.

The Tier 2 method to estimate CO2 emissions is based on the carbon mass balance approach, using national
statistical data on the inputs and outputs of carbonaceous materials to coke production. Where country-specificcarbon content data derived from national fuel characteristics are available, it is good practice to use them.
Otherwise, a hybrid methodology 2 can be used, selecting the default carbon content data provided in Table 4.3,
provided that coke production is not a key category, in which case country-specific data are required.
The Tier 3 method to estimate CO2 emissions requires plant-specific emissions measurement data or modelling
results, combined with plant-specific activity data and plant-specific carbon content data for the carbon massbalance approach, for those sources where measurement data are not available. Where models are used to estimate
emissions (for example, a model that combines a carbon mass balance with measurements), it is good practice toconduct model verification to present evidence to justify that the model outputs reflect the facility performance.
Further, it is good practice to fully document the data and assumptions applied within the model, the sensitivity ofthe model to key data and assumptions, and the associated uncertainty with modelling results.
Where stack emission measurements are used, it is good practice for inventory compilers to document the sampling
protocols and analytical methods applied, and to present supporting information to justify that the measurement
results reflect plant performance, such as information on the frequency and duration of the measurements, thevariability of the process and its GHG emissions and whether the plant was operating under normal conditions.

BOX 4.0 (NEW)FLARING ACTIVITIES IN METALLURGICAL COKE AND IRON AND STEEL PRODUCTIONS

Gaseous products from metallurgical coke and iron and steel production are mainly used for thegeneration of heat and electricity, and in some cases as reducing agents. There is a minor proportionof the total gas produced, usually less than 5 percent, which is lost from the production stream andflared, mainly during emergencies or consumer maintenance.
Integrated facilities usually flare a mix of the gases produced, including coke oven gas (COG), blast
furnace gas (BFG) and Linz-Donawitz (converter) Gas (LDG) [also known as basic oxygen furnacegas (BOFG)], at the same stacks. This situation represents a challenge for the GHG emissions
reporting, because:• GHG emissions from COG flaring should be reported under the Energy Sector;• GHG emissions from BFG and LDG flaring should be reported under IPPU.
Therefore, in an integrated steelworks, where flares of combined gases are occurred and therefore
the individual estimates for flaring of COG, BFG and LDG cannot be determined, then it is goodpractice to report all flaring emissions in IPPU to minimise the risk of double-counting, and to apply
methodologies that minimise the overall uncertainty in the inventory.
COG has a high energy content and losses to flaring are minimised as a result, to typically less than
2 percent of COG production.
BFG is also used widely for heat and power-raising, with flaring activity often determined by gas
demand on plant, and typically up to 20 percent flared. LDG may be captured and used around thefacility to meet fuel combustion demand, but is often completely flared and in some cases may bedirectly vented to atmosphere.
The typical industry flaring rates are: COG 0.3-2 percent; BFG 0.5-20 percent; LDG 5-100 percent.

2 ‘Hybrid’ refers to a methodology based on the complete carbon balance approach, with the use of default carbon content data.

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Table 4.1b summarizes the activity data and the emission factors to be used to estimate CO2 emissions for thedifferent Tiers.
TABLE 4.1B (NEW)TIERS TO ESTIMATE CO2 EMISSIONS FROM METALLURGICAL COKE PRODUCTION – NON FUGITIVE EMISSIONS
MethodAD

EFTechnology

Limitations/Comments

Tier

Productionbased

Metallurgicalcoke produced in
the country

Default
EF(Table4.1)

This method
can be applied
to technologies
with andwithout byproductrecovery.

The production-based
method should not be
used to estimate
emissions in conjunction
with the carbon balance
approach for iron andsteel production, where
the coke ovens operate
within an integrated
steelworks, to avoid
double-counting.

Tier 1a

Simplified
carbonbalance(where only
limited AD
are available)

Coking coalconsumed andmetallurgicalcoke produced in
the country

Carboncontent ofcokingcoal andcoke(Defaultsarepresented
in Table
4.3)

This method
assumes 100%
consumptionof COG within
the cokemakingprocess, thus it
is moreapplicable tocases whereby-products
are not
recovered.

If this method is applied,
do not also calculate CO2
emissions from fugitives
and flaring using themethods described in the
Energy volume, to avoid
double-counting.

Tier 1b

National
CarbonBalancemethod(countryspecific EFs)

National data on
all inputs (rawmaterials andfuels, i.e. cokingcoal) and on all
outputs (products
and by-products:
coke, COG, tars
and benzenes,
flaring)

Countryspecificcarboncontents
of inputs
and
outputsAll
technologies

If country-specific carbon
contents are not available
for all inputs and outputs,
the default carbon
contents from Table 4.3
may be applied with thehybrid method, but thiswill be considered a Tier
1 / Tier 2 approach which
is not appropriate for a
key category.

Tier 2Aggregatedplant-specificcarbonbalancemethod(countryspecific EFs)

Installation-level
data on all inputs(as describedabove) andoutputs (asdescribed above)

Plantspecificcarboncontents
of inputs
and
outputsAll
technologies

n/aTier 3aInstallationlevelmeasurement
data or plant
specificmodelling
data

n/a

n/a

All
technologies

Emissions measurement
data and/or modelling
results must be complete
for all emission sources atthe coke plant and mustcomply withmeasurement protocols
and/or verification
processes for modelling.

Tier 3b

The methodologies to estimate CH4 emissions relate to emissions from stacks, using default emission factors (Tier1a), country specific emission factors (Tier 2) or measurements/models (Tier 3). The methodology to estimate CH4
fugitive emissions is described in Section 4.3.2.2 Chapter 4 Volume 2 of the 2019 Refinement (IPCC category
1.B.1c).

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Chapter 4: Metal Industry Emissions

TIER 1 METHOD
Tier 1 a: Production based method
Applying this method requires the amount of coke produced (tonnes) in the country and a default emission factor,
given in Table 4.1. The following equations are used:

EQUATION 4.1 (UPDATED)CO2 EMISSIONS FROM COKE PRODUCTION (TIER 1A)= CK • EFCO2
ECO2 ,energy
EQUATION 4.1A (NEW)CH4 EMISSIONS FROM COKE PRODUCTION (TIER 1A)= CK • EFCH 4
ECH 4 , energy
Where:
ECO2,energy or ECH4,energy= emissions of CO2 or CH4 from coke production, in tonnes of CO2 or
tonnes CH4, to be reported under the Energy Sector, category 1.A.1c.

CK= quantity of coke produced nationally, tonnesEF= emission factor, tonnes CO2/tonnes coke produced or tonnes CH4/tonnes cokeproduced (Table 4.1)

Tier 1 b: Simplified carbon balance method
The Tier 1 b method assumes that all of the coke oven by-products are transferred off site and that all of the cokeoven gas produced is burned on-site for energy recovery. Applying this method requires data on the amount ofcoking coal used as raw material and the amount of metallurgical coke produced. The following equation, with adefault carbon content given in Table 4.3, is used:

EQUATION 4.1B (NEW)CO2 EMISSIONS FROM METALLURGICAL COKE PRODUCTION (TIER 1B)

ECO2 ,energy = (CC • Ccc − CK • CCK ) •44
12

Where:
ECO2,energy = CO2 emissions to be reported in the Energy Sector category 1.A.1c, tonnesCC= quantity of coking coal consumed for coke production in the country, tonnes

CK= quantity of coke produced in the country, tonnes

CCC= default carbon content of coking coal, tonnes C/tonne coal

CCK

= default carbon content of metallurgical coke, tonnes C/tonne coke

TIER 2 METHODThe Tier 2 method to estimate CO2 emissions is appropriate where national statistics on process inputs and outputs
from integrated and non-integrated coke production processes are available, and where country-specific carbon
contents for process inputs and outputs are available

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EQUATION 4.2 (UPDATED)CO2 EMISSIONS FROM METALLURGICAL COKE PRODUCTION

ECO2 , energy = [CC • CCC + ∑ (PM a • Ca ) + BG • CBG − CO • CCO
a− COG • CCOG − ∑ (COBb • Cb ) − E flaring ]* 44 / 12bWhere:
ECO2,energy = CO2 emissions to be reported in the Energy Sector category 1.A.1c, tonnesCC= quantity of coking coal consumed in the country, tonnes

PMa= quantity of process materials a, other than those listed as separate terms, i.e. natural gas, fueloil or converter gas, consumed in the country for metallurgical coke production, tonnes

BG= quantity of blast furnace gas consumed in coke ovens in the country, tonnes

CO= quantity of metallurgical coke produced in the country, tonnes

COG= quantity of coke oven gas produced but not recirculated and therefore not consumed formetallurgical coke production, tonnes

COBb= quantity of coke oven by-product b (e.g. COG, coal tar, light oil) produced, and eithertransferred offsite or to other facilities or flared, tonnes

Eflaring= CO2 emissions from flaring, tonnes, deducted from the carbon mass balance, as thecorresponding emissions are estimated as fugitive emissions using the methodology describedin Section 4.3.2.2 Chapter 4 Volume 2 of the 2019 RefinementCx= country specific carbon content of material input or output x, tonnes C/tonne material[“CX” is a generic term intended to cover parameters above such as “CCC” – coking coal; “CCO” –metallurgical coke; etc.]
If country specific carbon contents for all the input and output materials included in Equation 4.2 are not available,
default carbon content from Table 4.3 could be used. In this case the methodology is a hybrid between Tier 1 andTier 2, and is not appropriate if the metallurgical coke production is a key category.
For CH4, in Tier 2 methodology inventory compilers can use the amount of coke produced, in combination withcountry specific emission factor.

TIER 3 METHOD
Unlike the Tier 2 method, Tier 3 uses plant specific data, considering that plants can differ substantially in theirtechnology and process conditions.
Tier 3 comprises two approaches for CO2 and only one for CH4:•

For CO2 and CH4:-•

monitoring data or modelling of stack emissions, from both carbonisation and from fuel combustion;
flaring of COG is excluded, as it is included in Section 4.3. Chapter 4 Volume 2 of the 2019 Refinement(category 1.B.1c).

For CO2:-

the carbon mass balance approach, with plant-specific carbon contents of all the materials used andproduced.

If actual measured CO2/CH4 emissions data are available from all the stacks present in all the coke production
plants in the country, these data could be aggregated and used directly to account for the national emissions frommetallurgical coke production. The total national emissions will be equal to the sum of emissions reported fromeach facility. It is a good practice to apply QA/QC to the monitoring data, following the recommendations included
in Volume 1 Chapter 6 of the 2019 Refinement.
A Tier 3 approach for one or more plants could be combined with lower Tiers approaches for other plants to derivea national estimate. In case the plant-specific CO2 emissions data are not available for part or for all sources in the

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Chapter 4: Metal Industry Emissions

country, the CO2 emissions for the unmeasured sources could be estimated using plant specific activity data
applying a carbon mass balance with country specific carbon contents, using Equation 4.2.
Figure 4.6 (Updated) Estimation of CO 2 emissions from metallurgical coke production
Start

Are sufficientmeasurements with satisfactory
QC, or verified modelling studies
available to estimate emissions
accurately?

Yes

Are allsingle sources for all theexisting plants measured ormodelled?

Use measurements or modelling
resultsYes

Box 6: Tier 3b

No
No

No

Are
plant-specificinput-output material data
available for theunmeasured part of thesourcecategory?

Are
country-specificcarbon content available
for the unmeasured
part of the source
category?

Yes

Yes

Use measurements combinedwith a carbon balance approachby plant for the rest of thesourcesBox 5: Tier 3aNo
Are national
data on input-output
material data
available?

Are
country-specificcarbon content
available?

Yes

Yes

Use a carbon balance approach(eq. 4.2)
Box 4: Tier 2No
No

Is thisa key category?

Is thisa key category?

Yes

Get input-output
material data

No

Yes

Get countryspecific carbon
content
Use a carbon balance approachwith default carbon content(eq. 4.2)
Box 3: Hybrid Tier 1/Tier 2NoAre
national coke production
and coal consumption data
available?

Use the simplified carbon balance
approach with default carbon
content (eq. 4.1b New)Yes

Box 2: Tier 1.b
No

Is nationalcoke production data
available?
No

Yes
Get national cokeproduction data

Use default EFs from Table 4.1
and coke national production data
(eq. 4.1 and 4.1a new)Box 1: Tier 1.a

Notes:(1)
Measurements corresponding to fugitive emissions should be estimated and reported with the methodology described in Chapter 4 Volume 2 ofthe 2019 Refinement.

4.2.2.2

C HOICE OF METHOD : IRON AND STEEL PRODUCTION

This section outlines three Tiers for calculating CO2 and CH4 emissions and two Tiers N2O emissions from ironand steel production. Decision trees are presented in Figures 4.7, 4.8a, 4.8b and 4.8c.

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The Tier 1 method is based on national production data and default emission factors. The method derives estimatesof CO2 emissions based on assumptions regarding the quantity of material inputs to sinter production and to ironand steel production, rather than through use of more detailed activity data on process inputs. Therefore, themethod is associated with higher uncertainties, due to the reliance on these assumptions. Consequently, the Tier 1
method is only appropriate where sinter production and iron and steel production are not a key category(ies).
The Tier 2 method to estimate CO2 emissions is based on the carbon mass balance approach, using national
statistical data on the inputs and outputs of carbonaceous materials. Where country-specific carbon content data
derived from national fuel characteristics are available, it is good practice to use them. Otherwise, a hybrid
methodology 3 can be used, selecting the default carbon content data provided in Table 4.3, provided that iron andsteel production is not a key category, in which case country-specific data are required.
The Tier 3 method is based on the use of stack measurements and/or modelling results:
Where stack emission measurements are used, it is good practice for inventory compilers to document the sampling
protocols and analytical methods applied, and to present supporting information to justify that the measurement
results reflect plant performance, such as information on the frequency and duration of the measurements, thevariability of the process and its GHG emissions and whether the plant was operating under normal conditions.
Where models are used to estimate emissions, it is good practice to conduct model verification to present evidence
to justify that the model outputs reflect the facility performance. Further, it is good practice to fully document thedata and assumptions applied within the model, the sensitivity of the model to key data and assumptions, and theassociated uncertainty with modelling results.

METHODOLOGY FOR ESTIMATING CO 2 EMISSIONS
Tier 1 method – production-based emission factors
The Tier 1 approach for emissions from iron and steel production is to multiply default emission factors by national
production data, as shown in Equation 4.4. Because emissions per unit of steel production vary widely dependingon the method of steel production, it is good practice to determine the share of steel produced in different types ofsteelmaking processes, calculate emissions for each process, and then sum the estimates. Equation 4.4 considers
steel production from BOF, EAF, and Open Hearth Furnaces (OHF). In the event that activity data for steel
production for each process is not available, default allocation of total national steel production among these threesteelmaking processes is provided in Table 4.1 in Section 4.2.2.3.
Equation 4.5 calculates emissions from the blast furnace production of pig iron that is not converted into steel. It
is preferable to estimate emissions from this production separately because the emission factors for integrated ironand steel production (BOF and OHF processes) take into account emissions from both iron production and steel
production.
A blast furnace is a closed system into which iron-bearing materials (iron ore lump, sinter and/or pellets), additives(slag formers such as limestone) and reducing agents (i.e. coke) are continuously fed from the top of the furnace
shaft through a charging system that prevents the escape of BFG. A hot air blast, enriched with oxygen andauxiliary reducing agents is injected on the tuyere level providing a counter current of reducing gases. The air blast
reacts with the reducing agents to produce mainly carbon monoxide (CO), which in turn reduces iron oxides tometal iron. The liquid iron is collected in the hearth along with the slag and both are cast on a regular basis. The
liquid iron is transported in torpedo vessels to the steel plant, and the slag is processed to produce aggregate,
granulate or pellets. The blast furnace gas is collected at the top of the furnace. It is treated and distributed aroundthe works to be used as a fuel for heating or for electricity production. The vast majority of GHGs are emitted fromthe blast furnaces’ stove stacks where the combustion gases from the stoves are discharged.
The objective in oxygen steelmaking is to burn (i.e. oxidise) the undesirable impurities contained in the hot metal
feedstock. The main elements thus converted into oxides are carbon, silicon, manganese and phosphorus. The
purpose of this oxidation process is to reduce the carbon content to a specified level (from approximately 4 – 5
percent to typically 0.01 – 0.4 percent), adjust the contents of desirable foreign elements and to remove undesirable
impurities to the greatest possible extent, which are oxidised with the subsequent removal of the off-gas or slag.
During the process, a number of additives are used to adjust steel quality and to form slag. The major emission
point for GHGs from the BOF is the furnace exhaust gas that is discharged through a stack after gas cleaning. The
gases produced during oxygen blowing (converter gas) contain large amounts of carbon monoxide. In moststeelmaking plants, measures have been taken to recover the converter gas and use it as an energy source. The COrich flue-gas can be collected, cleaned and buffered for subsequent use as fuel. The carbon is removed as CO and3 ‘Hybrid’ refers to a methodology based on the complete carbon balance approach, with the use of default carbon content data.

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Chapter 4: Metal Industry Emissions

CO2 during the oxygen blow. Carbon may also be introduced to a much smaller extent from fluxing materials andother process additives that are charged to the furnace.

Figure 4.7 (Updated) Decision tree for estimation of CO 2 emissions from iron and steel
production
Start

Are sufficientmeasurements with satisfactory
QC, or verified modelling studies
available to estimate emissions
accurately?

Yes

Are allsingle sources for all theexisting plants measured ormodelled?

Use measurements ormodelling results

Yes

Box 5: Tier 3b

No
No

No

Are
plant-specificinput-output material data
available for theunmeasured part of thesourcecategory?

Are
country-specificcarbon content available
for the unmeasured
part of the source
category?

Yes

Yes

Use measurements combinedwith a carbon balance
approach by plant for the restof the sources
Box 4: Tier 3aNo
Are national
data on input-output
material data
available?

Are
country-specificcarbon content
available?

Yes

Yes

Use a carbon balance
approach (eq. 4.9 to 4.11)
Box 3: Tier 2No
No

Is thisa key category?

Is thisa key category?

Yes

Get input-output
material data

Yes

Get country-specificcarbon content

No

Box 2: Hybrid Tier 1/Tier 2

No

Are national
production data (1)available?
No

Use a carbon balance
approach with default carbon
content (eq. 4.9 to 4.11)

Yes

Get national cokeproduction data

Use national production
data (1) with• default EFs from Table
4.1a and 4.1b• (eq. 4.4 to 4.8 and 4.8a(New))• carbon contents for BFG
and LDG from Table 4.3
Box 1: Tier 1.b

Note:(1) National production data refers to the productions of (1) steel; (2) pig iron not processed into steel; (3) direct reduced iron; (4) sinter;(5) pellet; (6) blast furnace gas and (7) converter gas.

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Figure 4.8a (New)

Decision tree for estimation of CH 4 emissions from coke production

Start

Are actual
measurements withsatisfactory QC or sufficient
data available to estimate emissions using
rigorous emission source
models?

Yes

Use measurements ormodelling results
Box 3: Tier 3NoAre
country specificemission factors
available?

Yes

Use country specific Efs withnational metallurgical cokeroduction data (eq. 4.1.a)Box 2: Tier 2

No
Is this akeycategory1?
Yes

No

Use default EFs from
Table 4.2 with national
metallurgical coke production
data (eq. 4.1.a)Box 1: Tier 1

Collect data for the Tier 2
or Tier 3 method.

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Chapter 4: Metal Industry Emissions

Figure 4.8b (Updated) Decision tree for estimation of CH 4 emissions from iron and steel
production

Start

Are actual
measurements withsatisfactory QC or sufficient data
available to estimate emissions using
rigorous emission
Source models?

Yes

Use measurements ormodelling results.
Box 3: Tier 3

No

Are country
specific emission factors
available?

Yes

Use country specific EFs
with national production data (1)(eq. 4.12 to 4.14a)Box 2: Tier 2

No

Is this a key category1?

Yes

Yes

Use default EFs from Table 4.2
with national production data (1)(eq. 4.12 to 4.14a)Box 1: Tier 1

Collect data for the Tier 2
or Tier 3 method.
Note: (1) National production data refers to the productions of (1) sinter; (2) pig iron; (3) direct reduced iron; (4) blast furnace gas and (5)converter gas.

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Figure 4.8c (New)

Decision tree for estimation of N 2 O emissions from iron and steel
production
Start

Are
sufficient Measurementswith satisfactory QC, or verified
modelling studies available toestimate emissions
accurately?

Yes

Use measurements or modelling
results.
Box 2: Tier 3 b

NoCollect data for
the Tier 3 method.

Yes

Is this a key category1?
No

Are national
production data on
BFG and LDG
available?

Yes

Use default EFs from Table 4.3
with national production data (eq.
4.14b).
Box 1: Tier 1No
Get national
production data.

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Chapter 4: Metal Industry Emissions

Equation 4.6 calculates CO2 emissions from production of Direct Reduced Iron (DRI) for the Tier 1 method usinga CO2 emission factor.
In sinter plants CO2 emissions occur during fuel combustion in burners and as a result of leakages from the feedmaterials, including coke fines and other carbonaceous materials. It is good practice to estimate separately theemissions from national sinter production and national pellet production, using Equations 4.7 and 4.8. whichshould be used if the inventory compiler does not have detailed information about the process materials used. If
the process materials are known, emissions should be calculated using the Tier 2 method.
Equation 4.8a calculates CO2 emissions from blast furnace gas (BFG) and converter gas (LDG) flaring, consideringthat 20 percent (vol) of the BFG is removed from the production stream and then flared, and that all (100 percent)of the LDG is also flared. (see Box 4.0)
Total emissions are the sum of Equations 4.4 to 4.8 (including the Equation 4.8a).
EQUATION 4.4
CO2 EMISSIONS FROM IRON AND STEEL PRODUCTION (TIER 1)
Iron & Steel: ECO , non − energy = BOF • EFBOF + EAF • EFEAF + OHF • EFOHF
2

EQUATION 4.5
CO2 EMISSIONS FROM PRODUCTION OF PIG IRON NOT PROCESSED INTO STEEL (TIER 1)
Pig Iron Production: ECO , non − energy= IP • EFIP
2

EQUATION 4.6
CO2 EMISSIONS FROM PRODUCTION OF DIRECT REDUCED IRON (TIER 1)
Direct Reduced Iron: ECO2 , non − energy= DRI • EFDRIEQUATION 4.7
CO2 EMISSIONS FROM SINTER PRODUCTION (TIER 1)
Sinter Production: ECO , non − energy= SI • EFSI2

EQUATION 4.8
CO2 EMISSIONS FROM PELLET PRODUCTION (TIER 1)
Pellet Production: ECO , non − energy= P • EFP
2

EQUATION 4.8A (NEW)CO2 EMISSIONS FROM BFG AND LDG FLARING (TIER 1)

ECO2 , non −energy = BFG • ( EFCO2 ) BFG flaring + LDG • ( EFCO2 ) LDG flaring= BFG • ( RBFG flared • CCBFG •44
44) + LDG • ( RLDG flared • CCLDG • )1212Where:
ECO2, non-energy= emissions of CO2 to be reported in IPPU Sector, tonnes

BOF= quantity of BOF crude steel produced, tonnes

EAF= quantity of EAF crude steel produced, tonnes

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OHF= quantity of OHF crude steel produced, tonnes

IP= quantity of pig iron production not converted to steel, tonnes

DRI= quantity of Direct Reduced Iron produced nationally, tonnesSI= quantity of sinter produced nationally, tonnes

P= quantity of pellet produced nationally, tonnes

EFx= emission factor, tonnes CO2/tonne x produced

�EFCO2 ��EFCO2 �
BFG

BFG flaring
LDG flaring= emission factor, tonnes CO2/tonnes of BFG produced= emission factor, tonnes CO2/tonnes of LDG produced= blast furnace gas produced nationally, tonnes

LDG= converter gas produced nationally, tonnes

RBFG flared= rate of BFG removed from the production steam and then flared. If this data is notavailable, a default value of 0.2 can be assumed (see Box 4.0)

RBFG flared= rate LDG removed from the production steam and then flared. If this data is notavailable, a default value of 1.0 can be assumed (see Box 4.0)

CCBFG

= carbon content of blast furnace gas, tonnes C/tonne

CCLDG= carbon content of converter gas, tonnes C/tonne

In an integrated plant, the emissions from the combustion of blast furnace gas, coke oven gas and converter gas toproduce heat for different needs within the steelworks (rolling mills, hot rolling mill, plate mill, bar mill, coldrolling mill, coating, pipe) and to produce electricity at the internal power plant to cover the internal needs should
be reported under IPPU (see Section 4.2.2.5). The methodology for these estimations is described in Chapter 2
Volume 2 of the 2006 IPCC Guidelines.

Tier 2 method
The Tier 2 method is appropriate where the inventory compiler has access to national data on the use of processmaterials for iron and steel production, sinter production, pellet production and direct reduced iron production. In
addition, as discussed in Section 4.2.2.5, there are several other process inputs and outputs that could be considered
under Tier 2. This data may be available from governmental agencies responsible for manufacturing or energy
statistics, business or industry trade associations or individual iron and steel companies. The Tier 2 method willproduce a more accurate estimation compared to the Tier 1 method, as it considers the actual quantity of inputs
that contribute to CO2 emissions.
Total emissions are the sum of Equations 4.9, 4.10 and 4.11. for those processes that occur in the country.
EQUATION 4.9 (UPDATED)CO2 EMISSIONS FROM IRON AND STEEL PRODUCTION (TIER 2)

ECO2 ,non −energy= [ PC CPC + ∑ (COBa Ca ) + CI CCI + LCL + DCD + CE CCEa

+ ∑ (ObCb ) + COG CCOG − S CS − IP CIP − BFG CBFG ] 
b

44
12

EQUATION 4.10 (UPDATED)CO2 EMISSIONS FROM SINTER PRODUCTION (TIER 2)

CBR • CBR + COG • C COG + BFG • CBFG+ • 44
E CO 2 ,non − energy =  +
(
)
•
PM
C
a
a
 ∑
 12
 a

Where, for iron and steel production:

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Chapter 4: Metal Industry Emissions

ECO2, non-energy= emissions of CO2 to be reported in IPPU Sector, tonnesPC= quantity of coke consumed in iron and steel production (not including sinter production),
tonnes

COBa= quantity of onsite coke oven by-product a, consumed in blast furnace, tonnes

CI= quantity of coal directly injected into blast furnace, tonnes

L= quantity of limestone consumed in iron and steel production, tonnes

D= quantity of dolomite consumed in iron and steel production, tonnesCE= quantity of carbon electrodes consumed in EAFs, tonnesOb= quantity of other carbonaceous and process material b, consumed in iron and steel
production, such as sinter, steel and pig iron scrap or waste plastic, tonnes

COG= quantity of coke oven gas consumed in stationary combustion equipment in iron and steel
production (such as cowpers, pre-heating ladles etc.), tonnes (or other unit such as GJ.
Conversion of the unit should be consistent with Volume 2 Energy)S= quantity of steel produced, tonnes

IP= quantity of iron produced not converted to steel, tonnes

BFG= quantity of blast furnace gas transferred off site or to other facilities in an integrated plant,
tonnes (or other unit such as GJ. Conversion of the unit should be consistent with Volume
2 Energy)

Cx= carbon content of material input or output x, tonnes C/(unit for material x) [e.g., tonnes
C/tonne]

Where, for sinter production:
ECO2, non-energy= emissions of CO2 to be reported in IPPU Sector, tonnes

CBR= quantity of purchased and on-site produced coke breeze used for sinter production, tonnes

COG= quantity of coke oven gas consumed in sinter production, tonnes (or other unit such as
GJ. Conversion of the unit should be consistent with Volume 2 Energy)

BFG= quantity of blast furnace gas consumed in sinter production, tonnes (or other unit such
as GJ. Conversion of the unit should be consistent with Volume 2 Energy)PMa= quantity of process material a, other than those listed as separate terms, such as anthracite,
consumed for sinter production in integrated iron and steel production facilities, tonnes

Cx= carbon content of material input or output x, tonnes C/(unit for material x) [e.g., tonnes
C/tonne]Equation 4.11 calculates CO2 emissions from the production of direct reduced iron for the Tier 2 method based on
reducing agents consumption and its carbon contents. Emissions from DRI production are derived fromcombusting fuel, coke breeze, metallurgical coke or other carbonaceous materials.
EQUATION 4.11
CO2 EMISSIONS FROM DIRECT REDUCED IRON PRODUCTION (TIER 2)

ECO2 , non −energy= ( DRI NG • CNG + DRI BZ • CBZ + DRI CK • CCK ) •44
12

Where:
ECO2, non-energy= emissions of CO2 to be reported in IPPU Sector, tonnes

DRING= amount of natural gas used in direct reduced iron production, GJ

DRIBZ= amount of coke breeze used in direct reduced iron production, GJ

DRICK= amount of metallurgical coke used in direct reduced iron production, GJ

CNG= carbon content of natural gas, tonne C/GJ

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CBZ= carbon content of coke breeze, tonne C/GJ

CCK

= carbon content of metallurgical coke, tonne C/GJ

Note: Natural Gas has a double role, to provide heat and act as a reducing agent in DRI furnaces.
If country specific carbon contents for all the input and output materials included in Equations 4.9, 4.10 and 4.11
are not available, default carbon contents from Table 4.3 could be used. In this case, the methodology is a hybrid
between Tier 1 and Tier 2 and is not appropriate if the iron and steel production is a key category.

Tier 3 method
Unlike the Tier 2 method, the Tier 3 method uses plant specific data. The Tier 3 method provides an even moreaccurate estimate of emission than the Tier 2 method because plants can differ substantially in their technology
and process conditions. If actual measured CO2 emissions data are available from iron and steelmaking facilities,
these data can be aggregated to account for national CO2 emissions. If facility-specific CO2 emissions data are notavailable, CO2 emissions can be calculated from plant-specific activity data for individual reducing agents, exhaustgases, and other process materials and products. The total national emissions will equal the sum of emissions
reported from each facility. Equations 4.9 through 4.11 describe the parameters that are necessary for an accountingof plant-specific emissions using the Tier 3 method and plant-specific activity data at a facility level. Plant-specificcarbon contents for each material are required for the Tier 3 method.

METHODOLOGY FOR CH 4
When carbon-containing materials are heated in the furnace for sinter production or iron production, the volatiles,
including methane, are released. With open or semi-covered furnaces, most of the volatiles will burn to CO2 above
the charge, in the hood and off-gas channels, but some will remain un-reacted as CH4 and non-methane volatileorganic compounds (NMVOC). The amounts depend on the operation of the furnace. Sprinkle-charging will
reduce the amounts of CH4 compared to batch-wise charging. Increased temperature in the hood (less false air)will reduce the content of CH4 further.
This section describes a Tier 1 default method and a more advanced Tier 2 and Tier 3 methods for CH4 emissions
from iron and steel production.
The Tier 1 method covers CH4 emissions from sinter production and from iron production, multiplying default
emission factors by national production data. Emissions from flaring are consider negligible, as CH4 in blast
furnace gas and in converter gas not significant. The guidance in this section does not cover the release of CH4
from pelletisation, although the associated emissions may be relevant when anthracite is used. CH4 may be emitted
from steel making processes as well, however those emissions are assumed to be negligible.
Equation 4.12 calculates CH4 emissions from sinter production, Equation 4.13 from pig iron production andEquation 4.14 from direct reduced iron production.
The total CH4 emissions are the sum of Equations 4.12, 4.13, 4.14 and 4.14a, for the processes that occur in the
country.

EQUATION 4.12
CH4 EMISSIONS FROM SINTER PRODUCTION (TIER 1)
Sinter Production: ECH , non − energy= SI • EFSI
4EQUATION 4.13
CH4 EMISSIONS FROM BLAST FURNACE PRODUCTION OF PIG IRON (TIER 1)
Pig Iron Production: ECH 4 , non − energy= PI • EFPI

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Chapter 4: Metal Industry Emissions

EQUATION 4.14
CH4 EMISSIONS FROM DIRECT REDUCED IRON PRODUCTION (TIER 1)
Direct Reduced Iron Production: ECH , non − energy= DRI • EFDRI
4

Where:
ECH4, non-energy= emissions of CH4 to be reported in IPPU Sector, kg

SI= quantity of sinter produced nationally, tonnesPI= quantity of iron produced nationally including iron converted to steel and not converted
to steel, tonnes

EFSI= emission factor for sinter production, kg CH4/tonne sinter produced

EFPI= emission factor for pig iron production, kg CH4/tonne pig iron produced

EFDRI= emission factor for steel by direct reduced iron production, kg CH4/tonne DRI steel
produced

In Tier 2 methodology inventory compilers can use the amount of sinter, pig iron from blast furnace and iron fromdirect reduction produced nationally, in combination with the corresponding country specific emission factors.
The Tier 3 method uses plant specific emissions data from stack emissions monitoring, or modelling results. The
total national emissions will equal the sum of emissions reported from each facility.

METHODOLOGY FOR N 2 O
This section describes a Tier 1 default method and a more advanced Tier 3 plant level method for N2O emissions
from iron and steel production. There is no Tier 2 method.
The Tier 1 method covers only N2O emissions from flaring, multiplying default emission factors by national
production data. The guidance in this section does not cover the release of N2O from other processes, as theseemissions are assumed to be negligible.
Equation 4.14b calculates N2O emissions from blast furnace gas (BFG) and converter gas (LDG) flaring,considering that 20 percent of the BFG is removed from the production stream and then flared, and that all (100percent) of the LDG is also flared (see Box 4.0).

EQUATION 4.14A (NEW)N2O EMISSIONS FROM FLARING (TIER 1)
BFG and LDG flaring:

EN2O , non −energy =BFG • RBFG flared • EFN2O BGF flared+ LDG • RLDG flared • EFN2O LDG flared

Where:
EN2O, non-energy= emissions of N2O to be reported in IPPU Sector, tonne

BFG= blast furnace gas produced, tonne

LDG= converter gas produced, tonne

RBFG flared= rate of BFG removed from the production steam and then flared. If this data is notavailable, a default value of 0.2 can be assumed (see Box 4.0)

RBFG flared= rate LDG removed from the production steam and then flared. If this data is not available,
a default value of 1.0 can be assumed (see Box 4.0)

EFN2O BFG flared = emission factor for BFG flared, tonne N2O/tonne BFG produced
EFN2O LDG flared = emission factor for LDG flared, tonne N2O/tonne LDG produced

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The Tier 3 method uses plant specific emissions data or modelling results.
The total national emissions will equal the sum of emissions reported from each facility.

4.2.2.3

C HOICE OF EMISSION FACTORSThis section provides default emission factors for CO2 and CH4 to be used in Tier 1a and provides a discussion on
carbon contents to be used in the carbon balance approach at higher Tiers.

TIER 1A METHOD
Carbon dioxide emission factors
Tables 4.1, 4.1a, 4.1b provide default emission factors for coke, sinter, pellet, iron and steel production from directemission sources. The emission factors for the three steelmaking methods are based on measurements and expert
judgment using typical practice for the different steel production scenarios.
Table 4.1 includes CO2 emission factors for both coke production technology types, i.e. with and without byproduct recovery. In the first case, the CO2 EF 0.51 t CO2/t coke was calculated as the mean value from the wide
range of sources analysed and chosen to be the Tier 1 EF as a conservative factor, not comprising energy saving
technologies, such as Coke Dry Quenching (CDQ), Coal moisture control etc. If these energy efficiency
technologies are in use at a country´s coke plants, the inventory compiler may choose a lower EF, e.g. 0.30 t CO2/t
coke. The wide range for by-product recovery coke plants, whose variability reflects not only different operationaland maintenance practices, but also, and foremost, the types of fuels used as primary for coke production (including
different combinations of coal, natural gas, fuel oil, coke oven gas, converter or blast furnace gas and other fuels).

TABLE 4.1 (UPDATED)TIER 1 DEFAULT CO2 EMISSION FACTORS FOR COKE PRODUCTION
Process

Emission Factor

SourceCoke production using byproduct recovery technology(tonne of CO2/tonne of coke)

0.51- (EU IPPC BREF 2013), Table 5.2, p.224 (0.16-0.86 t CO2/t
coke)- (Official Journal of the European Union 2011) (0.286 t CO2/t coke)- (Fruehan et al. 2000), Table A-10, p.33 (0.3-0.34 t CO2 /tcoke)- (US EPA 2012), section D.2.5, p.D-9 (0.21 tCO2/ t coke)- (Zhang et al. 2012), Table 4, p.2026 (0.518 t CO2 /t coke)

Coke production without byproduct recovery (tonne of
CO2/tonne of coke)

1.23- (US EPA 2012), section D.2.5, p.D-9

Table 4.1a includes CO2 default emissions factor for sinter production, which represents the mean value based on
the sources studied and refers to sinter plants which do not use carbonate ores. However, for those sinter plants
which do use carbonate ores this CO2 EF average can be up to twice as high. Moreover, this value can also vary
widely depending on the kind of fuel gases used in the ignition oven.
For pellet production the scarce set of CO2 EFs reported present a wide range of values. The default EF for Tier1
approach, included in Table 4.1.A, has been chosen as the maximum value reported. Similarly, for EAFs the CO2
EF chosen corresponds to the maximum value reported.

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Chapter 4: Metal Industry Emissions

TABLE 4.1A (NEW)
TIER 1 DEFAULT CO2 EMISSION FACTORS FOR SINTER AND PELLET PRODUCTION
Sinter production(tonne of CO2/tonne of sinter)

0.21- (Fruehan et al. 2000), Table 4.1 (0.17-0.19 t CO2/t sinter)- (Zhang et al. 2012), Table 4, p.2026 (0.21 t CO2/t sinter)- (EU IPPC BREF 2013), Table 3.4, p.96 (0.162-0.368 t CO2/t
sinter)- (Official Journal of the European Union 2011) (0.171t CO2/ tsinter)Pellet production (tonne
CO2/tonne pellet produced)

0.19- (EU IPPC BREF 2013), Chapter 4, Table 4.1, p.188

TABLE 4.1B (NEW)
TIER 1 DEFAULT CO2 EMISSION FACTORS FOR IRON AND STEEL PRODUCTION
Iron production(tonne CO2/tonne of hot metal)

Direct Reduced Iron production(tonne CO2 per tonne DRI
produced)

1.43

0.70

- (Fruehan et al. 2000), Table A-11, p. 33 (1.447-1.559 t CO2/t
hot metal)- (Zhang et al. 2012), Table 4, p. 2026 (1.375 t CO2/t hot
metal)- (Official Journal of the European Union 2011), Annex 1,(1.328 t CO2/t hot metal)
Direct Reduced Iron Production: European IPPC Bureau(2001), Integrated Pollution Prevention and Control (IPPC)Best Available Techniques Reference Document on the
Production of Iron and Steel, December 2001, Table 10.1 Page
322 and Table 10.4 Page 331
http://eippcb.jrc.es/pages/FActivities.htm

Steelmaking Method
Electric Arc Furnace (EAF)(tonne CO2/tonne of steel
produced) 1

0.18

Basic Oxygen Furnace (BOF)(tonne CO2/tonne of steel
produced) 2,3
1.58

Open Hearth Furnace (OHF)(tonne CO2 per tonne of steel
produced) 2,4

1.72- (EU IPPC BREF 2013), Chapter 8, Table 8.1, p.429 (0,0720,180 t CO2/t of steel produced)- (Fruehan et al. 2000), Table A-11, p.33. Comparison oftheoretical minimum and actual CO2 emissions for selected
processes comes up with a range of 0.189-0.207 t CO2/t liquid
steel, without considering blast furnace emissions- (Joint Research Center 2013), Table 7.3, p.369 (22.6-174 kg
CO2/t liquid steel), without considering blast furnace emissions
Steel Production: Consensus of experts and IISI Environmental
Performance Indicators 2003 STEEL(International Iron and Steel Institute, 2004)

1 The emission factor for EAF steelmaking does not include emissions from iron production. This factor is based on production of steel
from scrap metal, and therefore the EAF emission factor does not account for any CO2 emissions from blast furnace iron making.
Therefore is not applicable to EAFs that use pig iron as a raw material.
2 The emission factors for BOF and OHF steelmaking do include emissions from blast furnace iron production, and are consistent with
Equation 4.4
3 The emission factors for BOF represents the mean value of (Blast Furnace + BOF) CO

2emissions across the sources studied.

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Methane emission factors
Default CH4 emission factors are provided in Table 4.2 below.
TABLE 4.2 (UPDATED)TIER 1 DEFAULT CH4 EMISSION FACTORS FOR COKE PRODUCTION (NON FUGITIVES), IRON AND STEEL PRODUCTION
Process

Emission Factor

SourceCoke Production(kg CH4/tonne of coke produced)

0.089- (Japan NIR 2018) (0,089 kg CH4/t coke produced),- (Joint Research Center, 2013), Chapter 5, Table 5.2,
p.224 (0,001- 0,080 kg CH4/t coke produced)

Sinter Production(kg CH4/tonne of sinter produced)

0.07

EMEP/CORINAIR Emission Inventory Guidebook(EEA, 2005). Processes With Contact: Sinter andPelletizing Plants: Sinter and Pelletizing Plants (Except
Combustion 030301) Table 8.2a Emission factors forgaseous compounds

DRI Production
kg CH4/TJ (on a net calorific basis)

1

Energy Volume default emission factor for CH4Emissions from natural gas combustion. [See Table 2.3
of Volume 2, Chapter 2.]

Nitrous oxide
Due to the absence of emission factor values reported in literature, the approach described in US CRF 2018 (Title
40, Chapter I, Subchapter C, Part 98, Subpart W), that estimate N2O emission factors on the basis of CO2 emission
factors, is adopted. N2O emission factors estimated on the basis of this approach, are provided in Table 4.2b below.
TABLE 4.2B (NEW)
TIER 1 DEFAULT N2O EMISSION FACTORS FOR COKE PRODUCTION AND IRON AND STEEL PRODUCTION
Process

Emission Factor

Blast furnace gas flaring
tonnes N2O / tonnes BFG flared

1.4 E-06

Blast furnace gas flaring
tonnes N2O / GJ BFG flared

5.6 E-07

Converter gas flaring
tonnes N2O / tonnes LDG
flared

2.8 E-06

Converter gas flaring
tonnes N2O / GJ LDG flared

4.0 E-07

Source(EF CO2) BFG_flaring = 0.125 tonnes CO2/ tonnes BFG produced,(equation 4.8a, with CCBFG from Table 4.3) (1)Unit conversion made with 2.47 GJ/tonne of BFG(EFCO2) LDG_flaring = 0.257 tonnes CO2/ tonnes LDG produced,(equation 4.8a, with CCLDG from Table 4.3)1
Unit conversion made with 7,06 GJ/tonne of LDG

1

EFCO2 and EFN2O for oil and gas production are set as 3.0 E-03 and 3.3 E-08 Gg gas per 106 m3 gas produced, taken from Table 4.2.4.G
IPCC 2019 Refinement.

TIER 1B AND TIER 2 METHODS
The default carbon contents in Table 4.3 should be used if there is no information on average country specificcarbon contents. Carbon contents in Table 4.3 are based on expert judgment, complementing those provided inTable 1.2 and 1.3 in Chapter 1 Volume 2 of the 2006 IPCC Guidelines. It is a good practice to use country-specificvalues, based on measurements or other well-documented data. The Emission Factor Database (EFDB) provides
a variety of well-documented emission factors and other parameters that may be better suited to national
circumstances than the default values, although the responsibility to ensure appropriate application of material
from the database remains with the inventory compiler.

TIER 3 METHODSThe Tier 3 method is based on aggregated plant-specific emission estimates or the application of the carbon balance
approach at the plant specific level. The inventory compiler should ensure that each facility has documented theemission factors and carbon contents used, and that these emission factors are representative of the processes andmaterials used at the facility. The Tier 3 method requires carbon contents and production/consumption mass for
all process materials and off-site transfers such as those listed in Table 4.3. While this Table provides default
carbon contents, it is good practice under Tier 3 to adjust these values to reflect variations at the plant level. The

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Chapter 4: Metal Industry Emissions

carbon contents listed in Table 4.3 are only appropriate for the Tier 3 method if plant-specific information indicatesthat they correspond to actual conditions. It is anticipated that for the Tier 3 method the plant-specific data would
include both carbon content data and production/consumption mass rate data, and that therefore the default values
in Table 4.3 would not be applied to the Tier 3 method in most instances.
TABLE 4.3 (UPDATED)TIER 2 MATERIAL-SPECIFIC CARBON CONTENTS FOR IRON AND STEEL PRODUCTION (TONNES C/TONNE)
Process Materials

Carbon Content

Blast Furnace Gas

0.17

Charcoal*

0.91

BF injection coal

0.806

Steam coal (combustion coal)

0.671

Coal Tar

0.62

Coke

0.83

Coke Oven Gas

0.47

Coking Coal

0.73

Direct Reduced Iron (DRI, Gas-based)

0.020

Direct Reduced Iron (DRI,Coal-based)

0.020

Dolomite/Crude dolomite

0.13

EAF Carbon Electrodes1

1.00

EAF coal

0.89

Heavy oil

0.793Light oil

0.709

Kerosene

0.858

LPG

0.814

Hot Briquetted Iron 2

0.02

Limestone

0.121

Natural Gas

0.73

Oxygen Steel Furnace Gas or Converter gas

0.35

Petroleum Coke 2

0.87

Purchased Pig Iron

0.047

Scrap Iron 2

0.04

Steel Scrap and Steel2

0.01

Note:
1 Assuming 80 percent petroleum coke and 20 percent coal tar
2 Source: ISO14404-1 & ISO14404-2 with conversion from CO2 to C (multiplied by 12,011/44,01 as World Steel Association
calculates in the table 4).
* The amount of CO2 emissions from charcoal can be calculated by using this carbon content value, but it should be reported
as zero in national greenhouse gas inventories. (See Section 1.2 of Volume 1)

4.2.2.4

C HOICE OF ACTIVITY DATATIER 1 METHODThe Tier 1 method requires only the amount of steel produced in the country by process type, the total amount of
pig iron produced that is not processed into steel, and the total amount of coke, direct reduced iron, pellets, andsinter produced; in this case the total amount of coke produced is assume to be produced in integrated cokeproduction facilities. These data may be available from governmental agencies responsible for manufacturing
statistics, business or industry trade associations, or individual iron and steel companies. If a country only has

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aggregate data available, a weighted factor should be used. Total crude steel production is defined as the total
output of usable ingots, continuously-cast semi-finished products, and liquid steel for castings.

TIER 2 METHODThe Tier 2 method requires the total amount of iron and steel, coke oven gas, blast furnace gas, and processmaterials such as limestone used for iron and steel production, direct reduced iron production, and sinter productionin the country, in addition to onsite and offsite production of coke. These data may be available from governmental
agencies responsible for manufacturing or energy statistics, business or industry trade associations, or individual
iron and steel companies. These amounts can then be multiplied by the appropriate default carbon contents inTable 4.3 and summed to determine total CO2 emission from the sector. However, activity data collected at theplant-level is preferred (Tier 3). If this is not a key category and data for total industry-wide reducing agents andprocess materials are not available, emissions can be estimated using the Tier 1 approach.

TIER 3 METHODThe Tier 3 method requires collection, compilation, and aggregation of facility-specific measured emissions data
or facility-specific process material production/consumption mass data and carbon content data. The Tier 3 method
can be based on a plant-specific mass balance approach (for CO2 emissions) or on plant-specific direct emissions
monitoring data (for both CO2 and CH4 emissions). In this case, it is a good practice to apply a QA/QC for themonitoring data, following the recommendations included in Chapter 6 Volume 1 of the 2019 Refinement. The
Tier 3 method also may require activity data to be collected at the plant level and aggregated for the sectors. The
plant-specific data should preferably be aggregated from data furnished by individual iron and steel and cokeproduction companies. The amounts of process materials are more accurately determined in this manner. These
data may also be available from governmental agencies responsible for manufacturing or energy statistics, or frombusiness or industry trade associations. The appropriate amounts can then be multiplied by facility specific carbon
content data and summed to determine total CO2 emissions from the sectors, and the total emissions will be moreaccurate than when using the Tier 2 method. This approach also allows for additional accuracy by allowing
individual companies to provide more accurate plant-specific data and/or to use more relevant carbon contents thatmay differ from the default factors used in Tier 2 method.

4.2.2.5

C OMPLETENESSRELATIONSHIP TO THE ENERGY SECTOR
Iron and steel production consists of many production processes (occurring at different facilities), such as coking,sintering, iron-making, blast furnace steelmaking and rolling. These processes are connected to each other withthe pipeline network which carries by-product gases, such as coke oven gas, blast furnace gas and basic oxygen
furnace gas. This complexity creates the risk of double counting of emissions or omission of emissions.
Additionally, when there are many different types of steelworks in a particular country, it may be difficult to
calculate CO2 emissions for the Energy Sector and the Industrial Processes Sector separately without ambiguities.
Because of the dominant role of coke, it is important to consider the existence of coke making at a facility anddefine the boundary limits of the carbon balance at an iron and steelmaking facility to assure that CO2 emissions
are not double-counted. The combustion emissions from fuels obtained directly or indirectly from the feedstock
for an IPPU process will normally be allocated to the part of the source category in which the process occurs (seeBox 1.1 Chapter 1 Volume 3 of the 2006 IPCC Guidelines). Following this criterion, the emissions from iron andsteel production for the case of an integrated iron and steel plant should be reported under IPPU or under Energy,
as shown in Figure 4.8a. Note in particular:•

The emissions from the combustion of blast furnace gas, coke oven gas and converter gas for sintering in theblast furnace and for steel making should be reported under IPPU.

•

The emissions from the combustion of blast furnace gas, coke oven gas and converter gas to produce heat fordifferent uses within the steelworks (rolling mill, hot rolling mill, plate mill, bar mill, cold rolling mill,coating, pipe) should be reported under IPPU.

•

The emissions from the combustion of derived gases (including blast furnace gas, coke oven gas andconverter gas) to produce electricity in an internal power plant should be reported under IPPU•

Consistent with the guidance in Box 1.1. Chapter 1 Volume 3 of the 2006 IPCC Guidelines, where the derived
gases are exported off-site for subsequent combustion at another facility, (for example a nearby brick works
for heat production or a main electricity producer) then the emissions are reported in the appropriate source
subcategories (1A2f or 1A1a).

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Chapter 4: Metal Industry Emissions•

The emissions from flaring or venting of gases at coke ovens are allocated to the Energy (Fugitives) section
4.3.2.2 Chapter 4 Volume 2 of the 2019 Refinement, whilst the emissions from flaring or venting of gases
elsewhere in the Iron and Steel industry (e.g. blast furnace, sinter plant, basic oxygen furnace) are reported
under IPPU.

To avoid double counting and to ensure completeness it is a good practice to cross-check the proper allocation of
the emissions between the Energy and IPPU sectors, and to document where and how they are reported in theinventory.

RELATION TO OTHER METHODOLOGICAL APPROACHESIn the iron and steel industry there has been a global effort to establish a common methodology for the calculationof CO2 emissions and the energy intensity of steelworks as well as to conduct continuous data collection with the
purpose of performance tracking and promoting international cooperation in reducing CO2 emissions. The World
Steel Association established the first method of this kind in 2007, and since then, has conducted yearly
confidential CO2 data collection form steelworks across the world. The method was refined further and wasestablished as ISO 14404 “Calculation method of carbon dioxide emission intensity from iron and steel production”
in 2013. This methodology is appropriate for CO2 and energy management in the steel industry, and it is in linewith national policies of many governments. The calculation method establishes clear boundaries for the collectionof CO2 emissions data (Reference ISO 14404 “Calculation method of carbon dioxide emission intensity from ironand steel production”). The net CO2 emissions and production from a steel plant are calculated using all theparameters within the boundaries. The CO2 emission intensity is calculated as the net CO2 emission from the plantusing the boundaries divided by the amount of crude steel produced by the plant. With this methodology, the CO2
emission intensity of steel plants is calculated irrespective of the type of process used, products manufactured andgeographic characteristics. This calculation method only uses primary inputs to the plant and primary outputs fromthe plant that are commonly measured and recorded by the plants; thus, the method requires neither themeasurement of the specific efficiency of individual equipment or processes nor dedicated measurements of thecomplex flow and recycling of materials and waste heat. In this way, the calculation method ensures its simplicity
and universal applicability without requiring steel plants to install additional dedicated measuring devices or tocollect additional dedicated data other than those commonly used for plant management. Although the World Steel
Association does not recommend using these calculations to determine the benchmark for free allocation underemissions trading schemes (because different regions have different energy sources and raw materials available),the calculations can be used to compare the performance of steel plants globally and to help plant staff determine
their own position in energy and CO2 efficiency
There is a difference between the 2019 Refinement and ISO 14404 “Calculation method of carbon dioxide emission
intensity from iron and steel production”, dealing with the allocation of CO2 emissions to the IPPU and Energy
sectors, as in ISO 14404 the emissions from coking, sintering, blast furnacing, direct reduction, coke making
processes, reheating furnaces and rolling are reported under Energy, and only the emissions from the use of
limestone and dolomite are reported under IPPU.

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Subject to final copyedit and layout

Figure 4.8d (New)

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Energy or IPPU CO 2 emissions allocation in an integrated iron and steel facility

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OTHER FORMS OF CARBON
Although the dominant means of producing crude iron, or pig iron, is blast furnacing using coke, other forms ofcarbon (e.g., pulverized coal, coal derivatives, recycled plastics or tires, natural gas, or fuel oil) can also be used
to substitute for some portion of the coke in the blast furnace. In these cases, the materials should be accounted foras process sources of carbon in the same manner as coke, and care should be taken to deduct these materials fromany general energy statistics, if they are included there. Iron can also be produced in other types of iron-making
processes besides blast furnacing, such as direct reduced iron processes, often using natural gas or coal instead ofcoke, and these carbon sources should be accounted for in the same manner as coke, as they serve the same purpose.
In most blast furnaces, the iron making process is aided by the use of carbonate fluxes (limestone or dolomite).
Because these materials are necessary raw materials for the process, they should be accounted for as part of theiron and steelmaking inventory. Again, however, care should be taken not to double-count emissions associatedwith limestone and dolomite usage if accounted for separately in the minerals sector. (See Section 2.5, Other
Process Uses of Carbonates, in this volume.)

SINTER
Some integrated facilities also utilize sinter plants to convert iron-bearing fines into an agglomerate (or sinter)suitable for use as a raw material in the blast furnace. Typically, coke fines (or coke breeze) are used as a fuel inthe sintering process and are a source of CO2 and CH4 emissions. If the coke fines are produced at a coke plantwithin the facility and the CO2 and CH4 emissions are accounted for in the coal entering the facility, or if the cokebreeze is otherwise accounted for as purchased coke, the CO2 and CH4 emissions from coke used in sintering
should not be double-counted. Emissions from sinter production are categorised as IPPU emissions and should bereported as such.

EXHAUST GASESIt is important to avoid double counting blast-furnace-derived by-product gases such as blast furnace gas, or
recovered converter off-gas, if they have been accounted for as process emissions. Process emissions should
include all carbon inputs in the blast furnace, used as the primary reductant. In a typical fully integrated coke, ironand steel plant situation, adjustments may need to be made for coke oven by-products and the carbon content ofshipped steel, which should be clearly mentioned in the description of the sources. In some cases, it may also benecessary to make adjustments for blast furnace gas or iron that may be sold or transferred off site. The process
flow of exhaust gases is clearly illustrated in Figures 4.1-4.5.
The use of a default emission factor for CO2 emission estimates with Tier 1a for metallurgical coke production
and Tier 1 for iron and steel production assumes an average mix of fuel between coke oven gas, blast furnace gas
and, in some cases, converter off-gas. On the other hand, the Tiers based on the carbon balance approach consider
the actual flow of these gases used and produced. Therefore, the combined use of Tier 1a to estimate CO2 frommetallurgical coke production and Tier 2 or 3 to estimate CO2 from iron and steel production in integrated plants
can lead to double counting or underestimation of some of the gases used. Similarly, the combined use of Tier 1
to estimate CO2 from iron and steel production and Tier 2 or 3 to estimate CO2 from metallurgical coke production
can lead to double counting or underestimation of some of the gases used. The inventory compiler should take this
into consideration when choosing the Tiers to estimate CO2 emissions from integrated iron and steel plants.

ELECTRODE CONSUMPTIONElectrode consumption amounts to about 3.5 kg/tonne for EAF furnaces. However, depending upon thecharacteristics of the charged materials, some carbon may be added to the EAF (typically about 20 kg/tonne) forprocess control purposes or may be contained in the charged materials themselves as iron substitutes, anincreasingly more frequent trend. In these cases, CO2 and CH4 emissions from these additional carbon-bearing
materials should be considered process-related and accounted for in the inventory because their carbon content is
not as likely to have been accounted for elsewhere in the inventory. In addition, if natural gas is used to enhancereactions in an EAF as reducing agent it should be accounted for as a carbon source as all process materials usedin iron and steel manufacturing are reported as IPPU emissions.
Some specialty steel production takes place in electric induction furnaces, in which case the charge is 100 percent
steel scrap and where there are no carbon electrodes. There are no appreciable CO2 or CH4 emissions from thissteelmaking process.

OHF PROCESS
Although the OHF is no longer prevalent, it may be necessary to inventory CO2 and CH4 emissions from thissteelmaking process in some countries. An open hearth furnace is typically charged with both molten iron andscrap as in the case of a BOF, and oxygen is injected into the furnace, but reduction of carbon in the iron andmelting of the charge also takes place by firing fossil fuels (e.g., natural gas, fuel oil, coal or tar) across the surface

2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

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Volume 3: Industrial Processes and Product Useof the raw material bath. Carbon in the iron may be ignored, as in the case of the BOF, because it has beenaccounted for as a source of carbon for iron-making. However, carbon in the fuels used in the open hearth process
should be accounted for as IPPU emissions.

4.2.2.6

D EVELOPING A CONSISTENT TIME SERIESNo refinement.

4.2.3

Uncertainty assessment

The default emission factors for coke production and iron and steel production used in Tier 1 may have an
uncertainty of ± 10 percent. Tier 2 material-specific carbon contents would be expected to have an uncertainty of
10 percent. Tier 3 emission factors would be expected to be within 5 percent if plant-specific carbon content andmass rate data are available. Table 4.4 provides an overview of the uncertainties for emission factors, carbon
contents and activity data.
TABLE 4.4 (UPDATED)UNCERTAINTY RANGES
MethodData Source

Tier 1CO2 Default Emission Factors
CH4 Default Emission Factors
N2O Default Emission Factors
National Production Data
Material-Specific Default Carbon Contents± 10%± 400%± 300%± 10%± 10%

Tier 2

Material Country Specific Carbon Contents
National Reducing Agent & Process Materials Data

± 10%
± 10%

Tier 3Company-Derived Process Materials Data
Company-Specific Measured CO2 and CH4 Data
Company-Specific Emission Factors

± 5%
± 5%
± 5%

4.2.4

Uncertainty Range

Quality Assurance/Quality Control (QA/QC),
Reporting and Documentation

No refinement.

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2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 4: Metal Industry Emissions

4.3

FERROALLOY PRODUCTION

No refinement.

2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

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Volume 3: Industrial Processes and Product Use

4.4

PRIMARY ALUMINIUM PRODUCTION

This sub-chapter 4.4 “Primary Aluminium Production” Chapter 4 Volume 3 of the 2019 Refinement is an updateof sub-chapter 4.4 Chapter 4 Volume 3 of the 2006 IPCC Guidelines and should be used instead of the sub-chapter
4.4 in the 2006 IPCC Guidelines, with two exceptions relating to accounting of CO2 emissions from the primaryaluminium smelting process:•Section 4.4.2.1 – ‘Choice of method for CO2 emissions from primary aluminium production’,•Section 4.4.2.2 – ‘Choice of emission factors for CO2 emissions from primary aluminium production’.

For these two sections, the existing 2006 IPCC Guidelines should be used. No refinements have been made to
guidance on CO2 emissions from primary aluminium smelting.
Updates and new guidance since the 2006 IPCC Guidelines include the following:•

Section 4.4.1 is an updated introduction to GHG emissions from primary aluminium production, includingalumina refining via alternative Bayer-Sinter and Nepheline technologies.

•

Sections 4.4.2.3 to 4.4.2.7 and sections 4.4.3 to 4.4.4 provide new and updated guidance for accounting of
perfluorocarbon (PFC) emissions from the primary aluminium smelting process.
(i)
(ii)

(iii)
(iv)
(v)
(vi)
(vii)
•

Sections 4.4.5 to 4.4.7 provide new guidance on accounting GHG emissions from alumina production via
alternative refining processes: ‘Bayer-sintering parallel’ (BSP), ‘Bayer-sintering sequential’ (BSS) and‘Nepheline processing’ (NP) processes:
(i)
(ii)

4.38

Updated technology classes – addition of ‘PFPBL’, ‘PFPBM’, ‘PFPBMW’ – to replace the ‘CWPB’class in existing 2006 IPCC Guidelines for accounting PFC emissions only. For accounting of CO2
emissions from primary aluminium smelting, the ‘CWPB’ class should still be used.
Updated guidance (including updated Tier 1 and Tier 2 default factors and uncertainties) on PFC
emissions from ‘high voltage anode effects’ (HVAE), previously termed ‘anode effects’ in the 2006
IPCC Guidelines. This includes new Tier 2b and Tier 3b methods for estimating PFC emissions from
HVAE, using individual anode effect durations, rather than overall anode effect performance.
Existing methods based on overall anode effect performance have been relabelled as Tier 2a and Tier
3a.
New guidance on PFC emissions from ‘low voltage anode effects’ (LVAE), using either default (Tier
1) or facility-specific (Tier 3) emission factors.
New guidance on accounting PFC emissions during cell start-up (CSU) periods.
New guidance on Total PFC emissions, being the sum of HVAE, LVAE and CSU emissions (ifapplicable).
A new Tier 3DM facility-specific method for total PFC emissions by direct gas measurement.
Corresponding updates relating to Time-Series Consistency, Uncertainty Assessment and QA/QC
Reporting and Documentation sections.

This includes a Tier 1 and facility-specific Tier 3 method to account for CO2 emissions for BSP, BSS
and NP production routes.
Note that no new guidance is required for the alumina production via the conventional ‘Bayer’process.

2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 4: Metal Industry Emissions

4.4.1

Introduction to Primary Aluminium

This section covers emissions from primary aluminium production processes including, alumina refining using theBayer-Sinter and Nepheline alternative refining technology 4. A number of refinements and updates have been
made to the 2006 IPCC Guidelines and are detailed in the following sections.
Primary aluminium production typically begins with the mining of aluminium-containing ores (bauxites). Most
bauxite is refined through the Bayer Process, which thermo-chemically extracts aluminium oxide (alumina) fromthe ore. The main sources of greenhouse gas emissions from the Bayer Process are covered by existing guidancein the 2006 IPCC Guidelines for lime production (Volume 3, Section 2.3) and fossil fuel combustion associatedwith alumina hydrate calcination and heat production for hydrochemical processes (Volume 2: Energy). A small
proportion of alumina (<3 percent in 2015) is produced from the Bayer-Sinter process or nepheline ore refining
process using alternative technology. New guidance has been included in this chapter for emissions from subprocesses related to the Bayer-Sinter process and nepheline ore processes only.
Alumina is reduced to molten aluminium metal via the electrolytic Hall-Héroult process. In this process,electrolytic reduction cells can differ in the form and configuration of the carbon anode and alumina feed system
and are typically grouped by technology accordingly. In the 2006 IPCC Guidelines, four technology types were
defined, representing the technology in place at the time (percent global production): Centre-Worked Prebake –CWPB (82 percent including Point-Fed Prebake, PFPB), Side-Worked Prebake – SWPB (2 percent), Horizontal
Stud Søderberg – HSS (3 percent) and Vertical Stud Søderberg – VSS (13 percent).
Since 2006, the technological landscape has changed, a result of the closure of older technology facilities andsignificant investment in new, larger state-of-the-art facilities. Point-Fed Prebake Technology for example has
increased from <80 percent share of global production in 2006 to >90 percent in 2017 but more significantly, thegrowth in technology without fully automated anode effect intervention strategies for PFC GHG emissions has
risen from <30 percent of global production in 2006 to >60 percent in 2017. As such, the technology types havebeen redefined as follows:
(i)
(ii)
(iii)

(iv)
(v)
(vi)

Legacy Point-Fed Prebake (PFPBL) – older cell designs with line currents of less than 350kA;
Modern Point-Fed Prebake (PFPBM) – new cell technologies 5 that operate at line currents in excess
of 350kA including: AP3X/AP4X, APXe/AP60, EGA DX and DX+;
Modern Point-Fed Prebake without fully automated anode effect intervention strategies for PFC
emissions (PFPBMW) – new cell technologies operating with large cells with line currents often inexcess of 350kA, with no automatic anode effect intervention capacity (refer to Box 4.1a description)or with non-standard HVAE definitions, i.e. where HVAEs are not counted until the cell voltage has
exceeded the threshold for 15 to as many as 120 seconds (Marks & Nunez 2018b; Wong et al. 2018)vs. 3 seconds for the rest of the industry (refer to Box 4.2 for typical definition);
Side-Worked Prebake (SWPB) technology;
Horizontal Stud Søderberg (HSS) technology; andVertical Stud Søderberg (VSS) technology.

The three new Prebake technology classes – PFPBL, PFPBM and PFPBMW – should be used for accounting of PFC
emissions from primary aluminium smelting, in place of the previous CWPB class in the 2006 IPCC Guidelines.
However, for accounting CO2 emissions from primary aluminium smelting, the previous CWPB class should still
be used.
Although smelting technology has changed somewhat, the most significant process emissions have not. They are:(i)

CO2 emissions from the consumption of carbon anodes in the reaction to convert aluminium oxide
to aluminium metal (for which no refinements are included in this update for primary aluminium
smelting);(ii)

Emissions of the PFCs, tetrafluoromethane (CF4) and C2F6 during process upset conditions known
as ‘anode effects’ (for which refinements for aluminium smelting are included in the following
sections).

Also emitted are less significant process emissions: CO, Sulphur Dioxide (SO2), and Non-Methane Volatile
Organic Carbon (NMVOC). Sulphur hexafluoride (SF6) is not emitted during the electrolytic process and is only
4 Emissions from the combustion of fossil fuels associated with primary aluminium production, bauxite mining, and aluminium

production from recycled sources are covered in Volume 2: Energy. Also, carbon dioxide emissions associated with the
production of electricity from fossil fuel combustion to produce aluminium are also covered in Volume 2.

5 Details on some of these newest cell technologies are available on the following references: (Bardai et al. 2009; Rio Tinto

Alcan 2013; Emirates Global Aluminium 2017)2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

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Volume 3: Industrial Processes and Product Use

rarely used when fluxing specialized, high magnesium aluminium alloys, from which small quantities can bereleased as fugitive emissions.

BOX 4.1A (NEW)FULLY AUTOMATED ANODE EFFECT INTERVENTION STRATEGIES FOR PFC EMISSIONS

Many Point-Fed Prebake (PFPB) aluminium smelters employ fully automated control strategies toreduce PFC emissions, otherwise known as ‘automatic anode effect intervention or termination’strategies. These are strategies that rapidly terminate high voltage anode effects (HVAE) when they
are detected, using both: (i) automated up/down movements of carbon anodes and (ii) automatedfeeding of alumina to rapidly increase dissolved alumina levels in the cell; in most cases, no manualintervention is required.
However, these automated strategies are not employed in one technology class – Modern Point-Fed
Prebake without fully automated anode effect intervention strategies for PFC emissions (PFPBMW)– where anode effects are terminated through manual operator intervention, which can result inhigher PFC emissions. This technology class is also characterised by the use of HVAE definitions
that differ significantly from that used in the rest of industry (see Box 4.2).

4.4.2

Methodological issues for primary aluminium
production

4.4.2.1

C HOICE OF M ETHOD FOR CO 2 EMISSIONS FROM PRIMARY

ALUMINIUM PRODUCTION
No refinement.

4.4.2.2

C HOICE OF EMISSION FACTORS FOR CO 2 EMISSIONS FROMPRIMARY ALUMINIUM PRODUCTION
No refinement.

4.4.2.3

C HOICE OF METHOD FOR PFC S

This section includes background and guidance on methods for estimating PFC emissions from different sources– ‘high voltage anode effects’ (HVAE) and low voltage anode effects (LVAE) – using a range of methods.

PFC EMISSIONS FROM ALUMINIUM PRODUCTION
During electrolysis, alumina (Al2O3) is dissolved in a fluoride melt comprising 80 percent by weight cryolite(Na3AlF6). Perfluorocarbons (PFCs) are formed from the reaction of the carbon anode with the cryolite melt during
a process upset condition known as an ‘anode effect’ (see Box 4.2). An anode effect occurs when the concentrationof alumina in the electrolyte is too low to support the standard anode reaction. When the 2006 IPCC Guidelines
were developed, anode effects were characterised by a sudden increase in voltage generally greater than 8V (USEPA 2008) for a period of approximately 3 seconds. These anode effects are now known as a ‘high voltage anodeeffects’ (HVAE), which release both CF4 and C2F6.

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Chapter 4: Metal Industry Emissions

BOX 4.2 (UPDATED)HIGH AND LOW VOLTAGE ANODE EFFECT DESCRIPTION

An anode effect is a process upset condition where an insufficient amount of alumina is dissolved in
the electrolyte, resulting in the emission of PFC gases. This often causes cell voltage to be elevatedabove the normal operating range. However, PFC gases can also be generated without elevated cellvoltage.
A high voltage anode effect (HVAE) is typically identified as an anode effect where the voltage
exceeds the specific voltage threshold defined at the facility for a specific duration. The typicalvoltage threshold of the industry, and used within this guideline, is 8 volts (Tabereaux 2004; US
Environmental Protection Agency & International Aluminium Institute 2008) while the typicalduration is 3 seconds (Wong et al. 2015).
A low voltage anode effect (LVAE) is typically identified as emission of PFC gases in cases where
the cell voltage does not exceed the voltage threshold.
Since the late 2000s, driven by the development of more productive, high-amperage cell technology with manylarge anodes, ‘low voltage anode effect’ (LVAE) emissions of CF4 have been identified. These LVAE emissions
have been the focus of much research and occur as result of the same process upset condition as HVAE emissions
but often at a smaller, localised scale. Guidance on estimating LVAE C2F6 emissions has not been provided hereas C2F6 concentrations from LVAE are most of the time undetectable (within the noise level of the measuring
instrument) or at low ppb levels. During LVAE, the cell voltage typically remains below the formation voltage of
C2F6. Some research (Asheim et al. 2014; Dion et al. 2016) has even concluded that formation of C2F6 from LVAE
does not occur, or occurs at levels so low, it is considered negligible.
LVAE emissions have not been included in national GHG inventories to date because the information andmethodology for their estimation was not available, but estimates should now be included to ensure GHG
inventories are as complete as possible.

CHOICE OF METHODOLOGIES FOR PFCS
It is good practice to estimate and report Total PFC emissions, i.e. the sum of HVAE and LVAE emissions
combined. The decision trees shown in Figures 4.12 and 4.12a describe good practice in choosing the PFC
inventory methodology appropriate for national circumstances for HVAE and LVAE, respectively. Table 4.14a
provides a summary of all methods in this guidance for estimating PFC emissions at Tiers 1 to 3. Note that themethodologies for HVAE and LVAE are presented separately to allow for different Tiers to be adopted for eachelement if necessary.
All inventory compilers in countries with aluminium production should be able to implement at least the Tier 1
method and thereby ensure completeness of reporting. Although this chapter presents default emission factors,
countries should make every effort to use higher Tier methods because emission rates can vary greatly, and theuncertainty associated with Tier 1 factors is very high. Most aluminium smelters routinely collect the process dataneeded for calculation of Tier 2 emissions factors. The sole exception is facilities with PFPBMW technology, whose
process data (specifically, accounting of HVAEs) is not currently compatible with the Tier 2 emission factors
presented here. For these smelters, it is still possible to implement Tier 3 methods – for example, production-based
emission factors (for HVAE and LVAE emission sources, or total PFC emissions) or direct PFC gas measurements(Tier 3DM). Furthermore, use of Tier 3 methods for HVAE emissions (based on HVAE performance) is also
possible for PFPBMW facilities, provided conventional definitions of HVAEs (refer to Box 4.2) are adopted.
For HVAE emissions, the Tier 1 method is based on aluminium production, while the Tier 2 (2a and 2b) and Tier
3 (3aHVAE and 3bHVAE) methods are based on plant-specific process data for HVAEs, which are regularly collectedby smelters. In choosing a method for estimating PFCs, it should be noted that the uncertainty associated withhigher tier methodologies is generally significantly lower than that for Tier 1, and therefore it is generally goodpractice to use Tier 2 and Tier 3 methodologies if this is a key category. There is an exception for countries where
the prevailing technology is PFPBMW, whose current definitions (and therefore accounting) of HVAEs are notcompatible with the Tier 2a, 2b, 3aHVAE, or 3bHVAE methods in this guidance. In these cases, the Tier 1 method is
acceptable for estimating emissions from HVAE even if the source is key, although use of Tier 3 methods (e.g.
production-based facility-specific factors, or direct measurement Tier 3DM) will significantly reduce uncertainty.
The Tier 3 methodologies for HVAE PFC emissions should be utilized with coefficients calculated frommeasurement data obtained using good measurement practices (US Environmental Protection Agency &International Aluminium Institute 2008). Communication with primary aluminium producers will determine theavailability of process data, which, dictates the method used to calculate emissions. Plants other than PFPBMW2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

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Volume 3: Industrial Processes and Product Use

routinely measure HVAE performance as ‘anode effect minutes per cell-day’. HVAE PFC emissions are directly
related to anode effect performance via a coefficient specific to technology or plant.
In the 2006 IPCC Guidelines, two methods for calculating coefficients for HVAE PFCs were outlined: slope andovervoltage. The overvoltage method is not widely used anymore so this update will focus on the slope method
only. If the overvoltage method is still used, it should be adopted at the Tier 3 level only. If Tier 3 is not possible
then it is good practice is to adopt the Tier 2a slope method.
For LVAE emissions, a Tier 1 method and two Tier 3 methods are provided. The Tier 1 method calculates PFC
emissions by multiplying technology-specific default emission factors by aluminium production. The first Tier 3
method calculates PFCs by multiplying a facility-specific factor (ratio of LVAE to HVAE emissions, based onprior measurements) by the HVAE emissions (Marks & Nunez 2018b). This takes into account plant-specificperformance at the HVAE level. The second Tier 3 method for LVAE uses a facility-specific, production-based
emission factor for LVAE emissions. There is currently no generally recognised means to calculate LVAE CF4emissions from the process control data that is normally recorded during primary aluminium production. The mostaccurate approach to date is to directly measure both LVAE and HVAE PFC emissions at the individual facility
level (Tier 3DM methodology for total PFC emissions), but this is not widely or regularly practiced by industry.
Moreover, there is currently no official methodology to standardise the measurement of LVAE PFC emissions.
Until an official methodology is released, the ‘Protocol for Measurement of CF4 and Hexafluoroethane (C2F6)
Emissions from Primary Aluminium Production’ ((US Environmental Protection Agency & International
Aluminium Institute 2008) can be used as guidance for total emissions measurement. It should be noted that there
is ongoing work within industry to provide an updated measurement protocol. The LVAE methodologies proposed
here provide a first step towards total emissions reporting but inventory compilers should be aware of the very
high level of uncertainty that accompanies these estimates and that work is ongoing within the aluminium industry
to provide good practice guidelines to complement these methodologies. It is good practice to check the EFDB asa source for future LVAE factors.
PFC emissions can also occur during cell start-up (CSU) – refer to Box 4.3 for a description. If they are not alreadyincluded in normal HVAE and LVAE accounting, then HVAE emissions during cell start-up can be estimated via
a Tier 2 approach (2bHVAE methodology, based on individual anode effect durations) or a Tier 3 approach using
facility-specific emission factors or coefficients (Tier 3aHVAE, 3bHVAE or 3CSU).
For all facilities, the Tier 3 approach is preferred because plant-specific coefficients will lead to estimates that are
more accurate. If no PFC measurements have been made to establish a plant-specific coefficient, the Tier 2 method
can be used until measurements have been made and Tier 3 coefficients are established. Countries can use acombination of methodologies depending on the type of data available from individual facilities.

ACCOUNTING FOR ALL SOURCES OF PFC EMISSIONSIn the following sections, a number of different methodologies with differing levels of uncertainty are proposed toestimate PFC emissions. To obtain the total respective emissions of CF4 and C2F6, the various sources of PFC
should be summed using Equation 4.24a. This equation is applicable for estimating total PFC emissions for all
Tier methods – the only exception being Tier 3DM direct gas measurement as this already provides total PFC
emissions from all sources.
EQUATION 4.24A (NEW)TOTAL PFC EMISSIONS

Total ECF4 = ( HVAE ECF4 + LVAE ECF4 + CSU ECF4 )and=Total EC 2 F6 ( HVAE EC 2 F6 + CSU EC 2 F6 )Where:

4.42

Total ECF4

= Total CF4 from aluminium production, kg CF4

Total EC2F6= Total C2F6 from aluminium production, kg C2F6HVAE ECF4= HVAE emissions of CF4 from aluminium production, kg CF4

HVAE EC2F6= HVAE emissions of C2F6 from aluminium production, kg C2F6

LVAE ECF4= LVAE emissions of CF4 from aluminium production, kg CF4

CSU ECF4= Total amount of CF4 produced during cell start-ups for a specific period, kg CF4

CSU EC2F6= Total amount of C2F6 produced during start-ups for a specific period, kg C2F62019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 4: Metal Industry Emissions

Note that the last terms in Equation 4.24a, CSU ECF4 = 0 and CSU EC2F6 = 0, where cell start-up emissions are
already accounted for by normal accounting of HVAE and LVAE emissions. Care should be taken neither to omit
nor to double count emissions from cell start-ups.

Figure 4.12 (Updated)

Decision tree for calculation of HVAE related PFC emissions fromprimary aluminium production

Start

Are process data
available?

Are
facility Specificcoefficients or factors
available per good practice1,
or can emissions bemonitored
directly?

Yes

No

Collect process data.

Yes

Calculate HVAE
PFC emissions using
Tier 3 method
Box 3: Tier 3No

No

Is the technology
class PFPBMW?

Yes

Is this a key
category1?

No

Is there an
automatic HVAE
termination
strategy?

Yes
No
Yes

Is the facility
using a standard HVAE
definition?

Yes

No

Are production
data available bytechnology?

No

Calculate HVAE
PFC emissions using
Tier 2 method
Box 2: Tier 2

Yes

Estimate annual production
by technology

Calculate HVAE
PFC emissions using
Tier 1 method
Box 1: Tier 1

Notes:
1
Good practices for obtaining facility specific PFC emission coefficients are detailed in the Protocol for Measurement of Tetrafluoromethane(CF4) and Hexafluoroethane (C2F6) Emissions from Primary Aluminum Production (US Environmental Protection Agency & International
Aluminium Institute 2008).
2
See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for
discussion of key categories and use of decision trees.

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Volume 3: Industrial Processes and Product Use

Figure 4.12a (New)

Decision tree for calculation of LVAE related PFC emissions fromprimary aluminium production
Estimate annual
production by technology.

No
Start
Are production data
available by technology?

Calculate LVAE PFC
emissions using Tier 1
method.

Yes

Box 1: Tier 1
Is the technology class
PFPBMW?

Yes

No
No

Is this a key
category3?

Are facility
specific productionbased EFs5 or LVAE/HVAE
ratios6 available per good practice2,
or can emissions bemonitored
directly?

Are HVAE PFC
emissions estimatedusing a Tier 1
method?

No

Yes

Obtain facility specific EFs5
or LVAE/HVAE ratios6 pergood practice2.

Calculate LVAE PFC
emissions using Tier 3
method.

Yes
No

Yes

Do not estimate LVAE PFC
emissions separately.1

Are facility
specific productionbased EFs5 or LVAE/HVAE
ratios6 available per good practice2,
or can emissions bemonitored
directly?

No

Box 2: Tier 3

Yes

Obtain facility specific EFs5
or LVAE/HVAE ratios6 pergood practice,2,4.

Notes:
1

LVAE PFC emissions are already accounted for in the Tier 1 default HVAE EF for PFPBMW.

Good practices for obtaining facility specific PFC emission coefficients are detailed in the Protocol for Measurement of Tetrafluoromethane(CF4) and Hexafluoroethane (C2F6) Emissions from Primary Aluminium Production (US Environmental Protection Agency & International
Aluminium Institute 2008).
2

See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for
discussion of key categories and use of decision trees.

3

Any PFPBMW facilities employing facility-specific coefficients for HVAE emissions are likely to have the necessary data to obtain facilityspecific coefficients or ratios for LVAE emissions.

45

To use the facility-specific production-based EF method (Equation 4.27c), metal production data from the facility must be available.

6

To use the facility-specific LVAE/HVAE ratio method (Equation 4.27d), HVAE emissions must be estimated first.

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Chapter 4: Metal Industry Emissions

TABLE 4.14A (NEW)SUMMARY OF ACCOUNTING METHODS FOR PFC EMISSIONS
Tier
1

2

3

Emission
SourcePFC
Gas

Method Description

By

Cell Technology
Applicable

1HVAE

HVAE

CF4,
C2F6

Production-based default
emission factor

Technology class

All technologies

1LVAE

LVAE

CF4

Production-based default
emission factor

Technology class

All technologies

2a HVAE

HVAE

CF4,
C2F6

Slope methoda,fTechnology class

All technologiesd
except PFPBMW

2b HVAE

HVAE

CF4,
C2F6

Non-linear methodb,cTechnology class

PFPBM, PFPBL and
SWPB only

3a HVAE

HVAE

CF4,
C2F6

Slopea or Overvoltagee
methodg

Facility specific

All technologiesd

3b HVAE

HVAE

CF4,
C2F6

Non-linear methodb

Facility specific

All technologiesd

3LVAE

LVAE

CF4

LVAE/HVAE ratio or
production-based factor

Facility specific

All technologies

3CSU

CSU

CF4,
C2F6

Cell start-up emission
factorFacility specific

All technologies

3DM

Total

CF4,
C2F6

Direct gas measurementh

Facility specific

All technologies

Notes:a

The slope method is where HVAE emissions are estimated based on overall anode effect performance.

Non-linear methods refer to the Tier 2b or 3b (Marks & Nunez 2018a) and (Dion et al. 2018a) methods, where HVAE emissions are
estimated based on individual anode effect measurement.
bcTier 2b methods for HVAE emissions are only applicable for PFPBM, PFPBL and SWPB technologies; alternative methods should be
used for VSS, HSS and PFPBMW technologies.

The Tier 2a/3a and 2b/3b methods for HVAE emissions are not applicable for PFPBMW technology, due to inconsistencies in defining an
HVAE. However, if consistent definitions (refer to Box 4.2) are adopted, then use of Tier 3a or 3b for PFPBMW technology is possible.

d

The overvoltage method is an alternative to the slope method, where HVAE emissions are estimated based on overall anode effectperformance; however this method should only be adopted a Tier 3 facility-specific level, since Tier 2 default emission coefficients havenot been updated here in the 2019 Refinement.

e

Use of the Tier 2a slope method for HVAE emissions during cell start-up (CSU) periods is possible, however, this may lead tooverestimates of emissions.
fg
To use the Tier 3a method for CSU emissions, it is good practice to use individual facility slope or overvoltage coefficients specificallyfor cell start-ups (as opposed to coefficients for normal operations, which may result in overestimates of emissions).
h
The Tier 3DM direct gas measurement method at individual facilities provides emission measurements that are inclusive of HVAE and
LVAE emissions during normal operations as well as CSU emissions (during cell start-up).

ESTIMATING EMISSIONS FROM HIGH VOLTAGE ANODE EFFECTS
Tier 1 method for High Voltage Anode Effect (HVAE) emissions: Use oftechnology-based default emission factors
The Tier 1HVAE method uses technology-based default emission factors for the main production technology types(Legacy PFPB, Modern PFPB, Modern PFPBMW, SWPB, HSS and VSS). PFC emissions can be calculated
according to Equation 4.25. The level of uncertainty in the Tier 1 method is much greater because individual
facility anode effect performance, which is the key determinant of anode effects and thus PFC emissions, is notdirectly taken into account. Tier 1 can be consistent with good practice when PFCs from primary aluminium is
not a key category, when pertinent process data are not available from operating facilities.
Tier 1 can also be consistent with good practice when the cell technology is PFPBMW as the process data required
for Tier 2 (e.g. anode effect frequency and duration) is typically not comparable to data for other technologies(Marks & Nunez 2018b) and could therefore lead to inaccurate results; however, if facility-specific emission
factors (e.g. production-based factors to use in Equation 4.25), coefficients or direct measurements (Tier 3DM) areavailable for PFPBMW technology facilities, it is good practice to adopt a Tier 3 method.

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EQUATION 4.25 (UPDATED)HVAE PFC EMISSIONS (TIER 1 METHOD)=
HVAE ECF4 ( HVAE EFCF4 • MP )and=HVAE EC 2 F6 ( HVAE EFC 2 F6 • MP )Where:HVAE ECF4= HVAE emissions of CF4 from aluminium production, kg CF4

HVAE EC2F6= HVAE emissions of C2F6 from aluminium production, kg C2F6HVAE EFCF4= default HVAE emission factor by cell technology type for CF4, kg CF4/tonne Al

HVAE EFC2F6 = default HVAE emission factor by cell technology type for C2F6, kg C2F6/tonne AlMP= metal production by cell technology type, tonnes Al

Tier 2a and Tier 3a methods for High Voltage Anode Effect (HVAE) emissions:
Based on overall anode effect performance and slope coefficient
The Tier 2a and Tier 3a methods estimate HVAE CF4 emissions based on the relationship between anode effectemissions and total anode effect minutes per cell-day. The slope coefficient is based on direct measurements of
PFCs. Tier 2a makes use of average coefficients from measurements at numerous facilities. Tier 3aHVAE is basedon measurements at the individual facility. Because the process mechanisms that produce PFC emissions during
HVAE are similar for CF4 and C2F6, the two gases should be considered together when estimating PFC emissions.
C2F6 emissions are calculated in the HVAE methods described herein as a fraction of CF4 emissions.
With an established relationship between anode effect process data and PFC emissions, process data collected on
an on-going basis can be used to calculate PFC emissions in lieu of direct measurement of PFCs. Equation 4.26
should be used when anode effect minutes per cell day are recorded. For individual high voltage anode effects, thereported anode effect duration (AED) is the sum of every second where the measured cell voltage is higher than
the trigger threshold. The anode effects minutes per cell day (AEM) are calculated based on the sum (in minutes)
of all the recorded anode effect minutes divided by the product of the number of cells in the considered section
and the respective time in days (US Environmental Protection Agency & International Aluminium Institute 2008).
Because PFPBMW smelters currently do not record shorter-duration anode effects that nevertheless can result insignificant PFC emissions, the Tier 2a and 3aHVAE methods are not recommended for PFPBMW smelters; however,if these facilities adopt consistent definitions for HVAEs (refer to Box 4.2), then it is possible to use Tier 3a.
Slope Coefficient: The coefficient characterises the kg of CF4 per tonne of aluminium produced, divided by anodeeffect minutes per cell-day 6. Since PFC emissions are measured per tonne of aluminium produced, it includes theeffects of cell amperage and current efficiency, the two main factors determining the amount of aluminium
produced in the cell. Equation 4.26 describes the method for both CF4 and C2F6.
EQUATION 4.26 (UPDATED)HVAE PFC EMISSIONS BY SLOPE METHOD (TIER 2A AND TIER 3A METHODS)

HVAE ECF4 =SCF4 • AEM • MP
and

HVAE
=
EC 2 F6 HVAE ECF4 • FC 2 F6 / CF4
Where:HVAE ECF4 = HVAE emissions of CF4 from aluminium production, kg CF4
HVAE EC2F6 = HVAE emissions of C2F6 from aluminium production, kg C2F6
SCF4

= slope coefficient for CF4 by cell technology type (Tier 2a) or smelter specific emission ratio(Tier 3a) (kg CF4/tonne Al)/(AE-Mins/cell-day)AEM= anode effect minutes per cell-day, AE-Mins/cell-day

6 The term ‘cell-day’ refers to the number of cells operating multiplied by the number of days of operation.

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Chapter 4: Metal Industry EmissionsMP= metal production, tonnes Al

FC2F6/CF4= weight fraction of HVAE C2F6/CF4, kg C2F6/kg CF4

Tier 3a method for High Voltage Anode Effect (HVAE) emissions: Based on
overall anode effect performance and overvoltage coefficient
Overvoltage Coefficient: Some process control systems characterize high voltage anode effects by calculating an
Anode Effect Overvoltage 7 (AEO) statistic. AEO is defined as the extra cell voltage above the target operating
voltage, and this parameter has been shown to be a good predictor of PFC emissions when recorded by the processcontrol system. The AEO process control technology is in use at a few modern smelters. AEO is calculated bysumming the product of time and voltage above the target operating voltage and dividing this figure by the timeover which data were collected. As noted above, for years beyond 2019, it is good practice to adopt this overvoltage
method only at a Tier 3 level; alternatively, if facility-specific overvoltage coefficients are unavailable, it is goodpractice to use the Tier 2a or 3aHVAE slope method.
EQUATION 4.27 (UPDATED)HVAE PFC EMISSIONS BY OVERVOLTAGE METHOD (TIER 3A METHOD)

HVAE ECF4 =
OVC •
and

AEO
• MP
CE /100

HVAE=
EC 2 F6 HVAE ECF4 • FC 2 F6 / CF4
Where:HVAE ECF4 = HVAE emissions of CF4 from aluminium production, kg CF4
HVAE EC2F6 = HVAE emissions of C2F6 from aluminium production, kg C2F6OVC

= Overvoltage coefficient for CF4, (kg CF4/tonne Al)/mV

AEO= anode effect overvoltage, mVCE= aluminium production process current efficiency expressed, percent (e.g., 95 percent)MP= metal production, tonnes Al

F C2F6/CF4= weight fraction of C2F6/CF4, kg C2F6/kg CF4

Tier 2b and Tier 3b method for High Voltage Anode Effect (HVAE) emissions:
Based on individual anode effect duration
An alternative way to quantify PFC emissions from HVAE for PFPB technology was proposed by (Marks &Nunez 2018a) and by (Dion et al. 2018a). This approach considers that the PFC generation rate is not constantthroughout the duration of the HVAE but declines as the HVAE continues. Therefore, PFCs are estimated for eachindividual HVAE (based on its duration) and the summation of individual HVAE emissions gives total HVAE
emissions.
In general, the Tier 2b method is expected to be more accurate than the Tier 2a method, and the Tier 3bHVAE method
is similarly expected to be more accurate than the Tier 3aHVAE method. The Tier 2b and 3bHVAE methods are
considered particularly useful for facilities with a low HVAE frequency or when considerable change in the
distribution of HVAE duration can be observed (e.g. years when an important relining and start-up of electrolysis
cells is expected). Both approaches quantify the PFC emissions from individual HVAEs based on processparameters that are known or calculated by the cell control system.
Tier 2b emission rate coefficients (K1, K2 for the Marks & Nunez 2018a method; C1, C2, C3 and C4 for the Dion etal. 2018a method) were calculated based on a set of data collected from different facilities. The Tier 3b
methodology uses the same equations as presented below with facility-specific coefficients, based on the results
7

Computer control systems report either ‘positive’ or ‘algebraic’ overvoltage depending on the version of software used. Useof the expression ‘overvoltage’ should not be confused with the classical electrochemical terminology, which usually means
the extra voltage needed for an electrochemical reaction to occur.

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Volume 3: Industrial Processes and Product Useof extensive gas monitoring measurement campaigns. A significant number of individual HVAE, with various
durations, should be monitored to obtain accurate coefficients. There is currently no measurement protocol
available to determine Tier 3 coefficients based on individual anode effect measurement but there is ongoing workwithin industry towards publication of an updated protocol.
The Tier 2b and 3bHVAE methods require extraction and use of performance data for individual HVAEs to calculate
PFC emissions (an alternative would be for cell control systems to automatically calculate and report total
emissions from individual HVAEs using the Tier 2b/3bHVAE methods). If HVAE performance data is unavailable,
an alternative method should be used.
At the Tier 2b level, the choice of method can be based on the following considerations:1.

Technology Class – The Marks and Nunez approach is applicable for PFPBL and PFPBM technologies; theDion et al. approach is applicable for PFPBM, PFPBL as well as the SWPB technology class. However,based on the lowest uncertainties for each technology (refer to Table 4.16b), the Marks and Nunez method
is recommended for PFPBL technology, whereas the Dion et al. approach is recommended for the PFPBM
and SWPB technology classes. For all other technology classes, it is good practice to employ facilityspecific Tier 3b coefficients or alternative methods.

2.

Distribution of individual HVAE durations (AED) at the facility – The Dion et al. approach is limited to
AEDs up to 1000 s for estimating CF4 and 150 s for C2F6, whereas the Marks & Nunez approach has theadvantage of no limitations on AED. Therefore, if a facility has a substantial proportion of HVAEs (e.g.
more than 5 percent) with AED greater than 150s, it is good practice to use the Marks and Nunez method
or alternative methods.

Marks & Nunez approach: The approach proposed by (Marks & Nunez 2018a) uses different coefficientsdepending on individual AED, as presented in Equation 4.27a. Note that for the Tier 2b approach, Tier 2b emission
rate coefficients (K1 and K2) are presented in Table 4.16a; these coefficients apply only to PFPBM and PFPBL
technologies. For Tier 2, weight fractions of C2F6/CF4 by technology class are given in Table 4.16 (these are thesame weight fractions as for the Tier 2a method).
EQUATION 4.27A (NEW)HVAE PFC EMISSIONS (TIER 2B AND TIER 3B METHOD – (MARKS & NUNEZ 2018A) )HVAE ECF4 =∑ [( K 1 • AEDiK2 ) •
and

kAi
]
1000

=
HVAE
EC 2 F6 HVAE ECF4 • FC 2 F6 / CF4
Where:HVAE ECF4= Total HVAE CF4 produced during the considered period, as the sum of all individual ‘i’
HVAE emissions, kg CF4

HVAE EC2F6= HVAE emissions of C2F6 from aluminium production, kg C2F6

AEDi

= Total duration of each individual ‘i’ HVAE, during which the cell voltage is above the
HVAE detection threshold, skAi= Average potline current during each individual ‘i’ HVAE, kA

K1= Emission rate coefficient dependant on the AED, dimensionless

K2= Emission rate coefficient dependant on the AED, dimensionless

FC2F6/CF4= weight fraction of HVAE C2F6/CF4, kg C2F6/kg CF4

Dion et al. approach: The approach proposed by (Dion et al. 2018a) to quantify total CF4 and C2F6, from thesum of emissions from individual HVAEs is presented in Equation 4.27b. Tier 2b emission rate coefficients(C1,C2,C3 and C4) are calculated using Equation 4.27f. Note that use of the Tier 2b emission rate coefficients are
only for (i) PFPBM and PFPBL and SWPB technology classes and (ii) HVAEs with durations (AED) below 1000s for CF4 estimation and below 150 s for C2F6 estimation, based on the data set used by (Dion et al. 2018a). For

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Chapter 4: Metal Industry Emissions

other technologies or longer duration HVAEs, it is good practice to employ Tier 3b coefficients or an alternative
method.

EQUATION 4.27B (NEW)HVAE PFC EMISSIONS (TIER 2B AND TIER 3B METHOD – (DION ET AL. 2018A) )HVAE ECF4 =∑ [(C 1 • AEDiC2 ) • MPDay ] / 1000
and

HVAE EC2 F6 =∑ [(C3 • AEDiC4 ) • MPDay ] / 1000

Where:HVAE ECF4= Total HVAE CF4 produced during the considered period, as the sum of all individual
HVAE emission, kg CF4

HVAE EC2F6= Total HVAE C2F6 produced during the considered period, as the sum of all individual
HVAE emission, kg C2F6

AEDi

= Total duration of each individual ‘i’ HVAE during which the cell voltage is above the
HVAE detection threshold, s

MPDay= Average daily metal production per cell 8, tonnes Al

C1= Emission rate coefficient for CF4 dependant on the metal production of the cell, g CF4 /stonne Al

C2= Emission rate coefficient for CF4 dependant on the metal production of the cell,dimensionless.

C3= Emission rate coefficient for C2F6 dependant on the metal production of the cell, g C2F6/stonne Al

C4= Emission rate coefficient for C2F6 dependant on the metal production of the cell,dimensionless.

ESTIMATING EMISSIONS FROM LOW VOLTAGE ANODE EFFECTS 9
Tier 1 method for Low Voltage Anode Effect (LVAE) emissions
The Tier 1LVAE method uses technology-based default emission factors for the main production technology types(PFPBL, PFPBM, SWPB, VSS and HSS). PFC emissions can be estimated according to Equation 4.27c. There is
no Tier 1LVAE default emissions factor for PFPBMW as an estimate for LVAE emissions is already included in the
Tier 1HVAE default emissions factor as this value was derived from total PFC measurement data. The level of
uncertainty in the Tier 1 method is much greater than the level of uncertainty in the Tier 3 methods because
individual facility operating characteristics are not taken into account. Tier 1 is consistent with good practice when
PFCs from primary aluminium is not a key category or when smelter specific LVAE emissions data are notavailable from operating facilities.

Day in Equation 4.27b is the average metal production per cell per day – it can be estimated from potline data or from theline amperage and average current efficiency of the potline. Care should be taken not to confuse this with the variable ‘MP’
– total metal production from the facility over the accounting period – used in other equations.

8 MP

9 C F emissions were not considered in the estimation of LVAE as C F concentrations from LVAE are most of the time
2 6
2 6

undetectable. The level of these emissions is in the low ppb and within the noise level of the measuring instrument. Some
research (Asheim et al. 2014; Dion et al. 2016) has even concluded that formation of C2F6 from LVAE does not occur, or
occurs at level so low, it is considered negligible.

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EQUATION 4.27C (NEW)
LVAE PFC EMISSIONS (TIER 1 AND TIER 3 METHODS – PRODUCTION-BASED)=LVAE ECF4 ( LVAE EFCF4 • MP )Where:
LVAE ECF4= LVAE emissions of CF4 from aluminium production, kg CF4

LVAE EFCF4= LVAE emission factor for CF4 (Tier 1 default by cell technology type, or Tier 3 facilityspecific), kg CF4/tonne AlMP= metal production by cell technology type, tonnes Al.

Tier 3 methods for Low Voltage Anode Effect (LVAE) emissions
The Tier 3 methods for estimating LVAE emissions multiply facility-specific factors either by (i) metal production(Equation 4.27c) or (ii) as a ratio of HVAE emissions (Equation 4.27d). The method based on metal production is
analogous to the Tier 1 method for LVAE. The method based on ratio of HVAE emissions assumes that HVAE
emissions reflect the overall performance and process control of the smelter. For both methods, it is good practice
to define the facility-specific emission factor (LVAE EFCF4), or emission ratio of LVAE to HVAE emissions(ER LV CF4) based on direct PFC measurements at the facility. Preliminary testing of both methods produced resultsthat were broadly aligned and consistent with the direct measurements of PFCs (Marks & Nunez 2018b).
A Tier 2 method for LVAE emissions has not been provided, since use of ERLV CF4 emission ratios for different
technology classes would not reduce uncertainty levels compared to a Tier 1 approach. This is because a Tier 2
ERLV CF4 emission ratio approach cannot capture all the underlying factors that drive LVAE emissions in one
smelter versus another of the same technology class. Therefore, this method is only recommended at a Tier 3
individual facility level.

EQUATION 4.27D (NEW)
LVAE PFC EMISSIONS (TIER 3 METHOD – AS RATIO OF HVAE EMISSIONS)

LVAE=
ECF4 HVAE ECF4 • ERLV CF4
Where:
LVAE ECF4= low voltage anode effect emissions of CF4 from aluminium production, kg CF4

HVAE ECF4= high voltage anode effect emissions of CF4 from aluminium production by cell
technology, kg CF4

ERLV CF4= Smelter-specific ratio of LVAE/HVAE CF4 emissions

ESTIMATING EMISSIONS FROM CELL START-UP
Tier 2 and 3 methods for Cell Start-Up (CSU) emissions
For completeness, it is good practice to always include CSU emissions (refer to Box 4.3) in total PFC emissions
estimates. There are various ways CSU emissions can be included depending on the methodological Tier selected.
The Tier 1 HVAE and LVAE default emission factors implicitly include CSU emissions; therefore, where the Tier
1 methods are used, there is no need to estimate CSU emissions separately. The Tier 2a and 2b HVAE methods
and the Tier 3a and 3bHVAE methods can account for CSU emissions if data on anode effect duration and frequency
are collected during CSUs and are included in the emissions calculations. As discussed below, this may lead to aslight overestimate of emissions if the Tier 2a or 3a slope factor method is used. Finally, the Tier 3DM direct
measurement method includes CSU emissions as long as the continuous emissions monitoring occurs during CSU
periods.

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BOX 4.3 (NEW)PFC EMISSIONS DURING START-UP OF ELECTROLYSIS CELLS

New electrolysis cells undergo a ‘start-up’ process prior to normal operation. The ‘start-up’ period
can vary from one facility to another, e.g. from the first few hours of a cell’s life to a month.
HVAEs can occur during start-ups of electrolysis cells – from the moment when the anode beam isfirst raised on the cell and metal starts being produced – leading to generation of PFC emissions(International Aluminium Institute 2006; Dando et al. 2008; Xu et al. 2008; Dando et al. 2009;
Maltais et al. 2010). While some researchers (Kristensen et al. 2007; Reny et al. 2016) have shownthat cell start-ups can be done without HVAE, it is not common practice and PFC emissions fromcell start-ups may contribute to a significant proportion of a facility’s total PFC emissions duringcertain periods, especially when the aluminium smelter is annually carrying out a large number ofcell start-ups.
While some facilities have historically included the start-up period in accounting HVAE emissions,others have excluded it given that it does not represent normal operations. It is thought that LVAE
emissions may also occur during the start-up period.
Furthermore, new cells following start-up typically operate with a higher cell voltage than during
normal operation. For this reason, some smelters use a different HVAE detection threshold (e.g. 9.5
volts instead of 8 volts) for a specific period to reduce the risk of falsely detecting HVAE (Dando etal. 2008). This detection threshold is specific to each facility (based on historical data) and should
be used for calculating HVAE performance at the facility when estimating cell start-up emissions
using any of the methods described here.
HVAE PFC emissions measured during CSU events have demonstrated lower emission rates than during normal
operations. For this reason, accounting for these HVAEs using the standard slope or overvoltage coefficient during
normal operations for the technology class (Tier 2a) or facility (Tier 3a) may lead to an overestimation of these
PFC emissions (Dando et al. 2008; Xu et al. 2008; Maltais et al. 2010).
To avoid overestimating emissions from CSUs through use of the Tier 2a or 3aHVAE methods, inventory compilers
have three options. Lowest uncertainties will be obtained with the second and third options presented below as
they are based on specific measurements during CSU. However, as a significant amount of CSU measurements
may prove difficult to acquire, it is good practice to consider the first option when no facility-specific data for cellstart-up is available. As a first option to take into consideration the different process dynamics of HVAEs during
the start-up of cells, compilers can use the Tier 2b or 3bHVAE non-linear approach (Equations 4.27a or 4.27b) when
no facility-specific measurement data for cell start-up is available. LVAE emissions during cell-start-up can thenbe estimated using either a production-based Tier 1 or Tier 3 approach (Equation 4.27c), or Tier 3 ratio of HVAE
emissions approach (Equation 4.27d).
As a second option, inventory compilers using the Tier 3a method can avoid overestimates by developing andapplying slope or overvoltage coefficients specifically for CSUs at the facility (in addition to the coefficients fornormal operation). Again, LVAE during start-up emissions may be estimated using a Tier 1 or Tier 3 approach.
The third alternative, when data is available, compilers may determine a facility-specific Tier 3 emission factor
based on the total emissions of PFC per cell start-up at the facility. This Tier 3CSU method accounts for both HVAE
and LVAE emissions during the start-up process, as given in Equation 4.27e:
EQUATION 4.27E (NEW)TOTAL PFC EMISSIONS FOR START-UP OF ELECTROLYSIS CELLS (TIER 3CSU METHOD)

CSU=
ECF4 ( EFCSU CF4 • N CSU )
And

CSU
=
EC 2 F6 ( EFCSU C F • N CSU )2 6

Where:
ECF4= Total amount of CF4 produced during start-ups for a specific period, kg CF4

EC2F6= Total amount of C2F6 produced during start-ups for a specific period, kg C2F6EFCSU_ CF4= Average amount of CF4 produced during the cell start-up period, kg CF4 / cell start-up

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EFCSU_ C2F6 = Average amount of C2F6 produced during the cell start-up period, kg C2F6 / cell start-up
NCSU= Total number of cell start-ups during the specific period considered, cell start-up

Note that Equation 4.27e should be used to estimate CSU emissions only if CSU emissions are excluded fromnormal HVAE and LVAE accounting. Care should be taken not to double count CSU emissions if they are alreadyincluded in the normal accounting of HVAE and LVAE emissions.

DIRECT MEASUREMENT OF TOTAL EMISSIONS
Tier 3 D M method for Total PFC emissions: Based on direct gas measurement
The Tier 3DM method is based on direct measurement of total PFC gases (CF4 and C2F6) at individual facilities,
rather than estimating emissions through emission factors or coefficients and process data (e.g. anode effectminutes per cell-day). As total emissions are measured, there is no need to account for PFCs from high and low
voltage anode effects (HVAE and LVAE) separately. Furthermore, cell start-up (CSU) emissions are included
since direct measurements should provide representative coverage of emissions from all operations. The Tier 3DM
method, following industry best practices, provides the lowest of uncertainty level for all accounting methods,
since the only sources of uncertainty is related to sampling procedures and measurement error.
Measurement approaches are only briefly described here. For detailed guidance on direct measurement of PFCs,
refer to established standard measurement practices and the latest industry protocols (e.g. (US Environmental
Protection Agency & International Aluminium Institute 2008)). The inventory compiler should also consult
guidance on plant-level measurements outlined in Volume 1, Chapter 2, and on QA/QC of measurements in
Volume 1, Chapter 6. Two approaches for direct PFC measurements are (i) time-integrated measurements and (ii)continuous measurements. While neither are routinely carried out by the industry at present, both have the potential
to provide continuous coverage of total emissions.
Time-integrated measurements are periodic measurements where PFCs from the facility are collected in sampling
containers over set time-intervals; gas samples are then analysed ‘off-line’ in a laboratory. Examples of analysis
techniques include: Gas Chromatography with Mass Spectrometry (GC/MS) and Fourier Transform Infrared
Spectrometry (FTIR). Time-integrated measurements are typically simpler and more cost-effective to operate andoften provide more accurate (with lower limits of detection) than continuous measurement approaches (USEnvironmental Protection Agency & International Aluminium Institute 2008; Fraser et al. 2013). For timeintegrated measurements, it is good practice to provide continuous coverage over time as this ensures
measurements are representative of all smelter operations. For more details, refer to the latest industry
measurement protocol for PFC measurements.
Continuous measurements are those where PFCs are measured continuously by in-situ instruments at the facility.
These have advantages of: (i) providing continuous coverage of total emissions and (ii) allowing emissions fromhigh vs. low voltage anode effects (HVAE and LVAE) to be accounted for separately (US Environmental
Protection Agency & International Aluminium Institute 2008). However, this approach can be more cost-intensive
and may require specialist expertise to operate and maintain. Examples of measurement techniques include: FTIR,
Mass Spectrometry (MS), Photoacoustic Spectrometry (PAS), Tunable-Diode Laser Absorption Spectrometry(TDLAS) and Quantum-Cascade Lasers (QCL) (Aarhaug et al. 2018). For accurate capture of LVAE emission
components, an important consideration is the detection limit of measuring instrumentation, given that LVAE
emissions are typically at low concentrations (as low as ppb levels); this introduces a further level of uncertainty
for continuous measurement approaches.
To ensure the accuracy of emissions accounting by direct measurement, it is good practice to employ establishedmeasurement practices and the latest industry protocols (US Environmental Protection Agency & International
Aluminium Institute 2008). There is ongoing work to develop an updated measurement protocol for total PFC
emissions (particularly LVAE emissions) to improve consistency and alignment across the industry.

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4.4.2.4

C HOICE OF EMISSION FACTORS FOR PFC S

Tier 1: Technology based default emission factors
Default emission factors for the Tier 1 method are provided in Table 4.15. These are for estimation of both HVAE
emissions (Equation 4.25) and LVAE emissions (Equation 4.27c). Aluminium production data by technology isusually available through national statistics publications or through publicly available company reports andwebsites.
Note that for the PFPBMW technology class, the HVAE-CF4 emission factor in Table 4.15 includes LVAE
emissions and therefore represents total CF4 emissions.
TABLE 4.15 (UPDATED)TECHNOLOGY SPECIFIC DEFAULT EMISSION FACTORS FOR THE CALCULATION OF HVAE AND LVAE EMISSIONS FROMALUMINIUM PRODUCTION (TIER 1 METHOD) (MARKS & NUNEZ 2018B)
Technology

HVAE

LVAE

CF4

C2F6

CF4

EFCF4
(kg/tonne Al)

Uncertainty
Range (%)b

EFC2F6(kg/tonneAl)

Uncertainty
Range (%)

EFCF4
(kg/tonneAl)

Uncertainty
Range (%)

PFPBL

0.016a-82/+126a

0.001-74/+109a

0.009a+99/-61

PFPBM

0.011

-90/+213

0.001-90/+256

0.018+247/-98

PFPBMW

0.161b-85/+476

0.013b-98/+864

-

-

SWPB

0.354

-76/+116

0.093-89/+68

0.010+69/-69

VSS

0.159c-94/+580c

0.009c-94/+525

0.001+61/-52

HSS

0.477

-79/+112

0.033-76/+860.026-dNotes:a
PFPBL emission factors and uncertainties reported in (Marks & Nunez 2018b) erroneously included data from another technology class(PFPBM). This has since been corrected in the emission factor and uncertainty values reported here (expert opinion – Dr Jerry Marks).
b

PFPBMW emission factor (EF) is based on total emissions measurement data which includes LVAE emissions.

c

VSS emission factors (EF) and uncertainties here incorporate data sets from (Marks & Nunez 2018b) and (Burkat, V.S. et al. 2018)d Single data point – no uncertainty range calculated.

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Tier 2a: HVAE-PFC emission factor based on technology specific relationshipbetween overall anode effect performance and PFC emissions
The Tier 2a slope method (Equation 4.26) is based on using technology specific coefficients for the applicablereduction cell and process control technology as listed in Table 4.16.
TABLE 4.16 (UPDATED)TECHNOLOGY SPECIFIC COEFFICIENTS FOR THE CALCULATION OF HVAE PFC EMISSIONS FROM ALUMINIUM
PRODUCTION USING SLOPE 10 METHODOLOGY (TIER 2A METHOD) (MARKS & NUNEZ 2018B)
Technology

CF4Weight Fraction C2F6/CF4SCCF4(kg CF4/tonne
Al)/(AEMins/cell-day) a

Uncertainty
Range (%)

C2F6/CF4

Uncertainty
range (%)

PFPBL

0.122

-48/+450.097-35/+31

PFPBM

0.104

-27/+320.057-55/+55PFPBMWa

-

-

-

-

SWPB

0.233

-27/+440.280-55+58VSS

0.058-53/+1300.086-76/+236

HSS

0.165

-47/+280.077-61/+48

Note:aTier 2 default coefficients are not available for PFPBMW technology class (Modern PFPB without fully automated anode effectintervention strategies for PFC emissions) because process data for anode effect frequency and duration was either not available, or, notcomparable to traditional definitions or thresholds associated with anode effects.

Tier 2b: HVAE-PFC emission rate coefficients based on individual anode effectdurationsMarks & Nunez approach: The Tier 2b method proposed by (Marks & Nunez 2018a) (Equation 4.27a) uses
different emission rate coefficients to estimate HVAE-CF4 emissions, based on the anode effect duration (AED)
of individual high voltage anode effects, as listed below in Table 4.16a.
For estimation of HVAE-C2F6 emissions, the Tier 2a technology-specific weight fractions of C2F6/CF4 (FC2F6/CF4)
should be used – refer to Table 4.16.
TABLE 4.16A (NEW)SPECIFIC HVAE-CF4 EMISSION RATE COEFFICIENTS BASED ON THE ANODE EFFECT DURATION AS CALCULATED BY(MARKS & NUNEZ 2018A) (TIER 2B METHOD).
AEDaaValue of K1

Value of K2

1s < AED ≤5s

0.0341

0.756

5s > AED≤200s

0.0473

0.693

AED >200 s

0.1661

0.479

In the rare occurrences where AED is equivalent to 0s, the equation that should be used is: kg CF4 = 0.576 · kA /1000

Dion et al. approach: For the Tier 2b method proposed by (Dion et al. 2018a) to calculate HVAE emissions(Equation 4.27b), emission rate coefficients C1, C2, C3 and C4 are defined in Equation 4.27f below for the genericsmelter, based on the daily metal production per cell.

10The ‘Overvoltage method’ (Equation 4.27) is no longer widely adopted within the aluminium industry. Therefore, there isinsufficient data available to update the overvoltage coefficients related to the overvoltage methodology. It is good practice
to compile PFC inventories using the slope model for recent and future calculations. Tier 3 overvoltage coefficients can still
be used as they are facility-specific (Dion et al. 2017; Marks & Bayliss 2012).

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EQUATION 4.27F (NEW)EMISSION RATE COEFFICIENTS FOR HVAE PFC (TIER 2B METHOD – (DION ET AL. 2018A) )C1 = 0.6415 • MPDay + 5.878
C2 =−0.0972 • MPDay + 0.8905=
C3 0.238MPDay 2 − 1.407 • MPDay + 2.342
C4 =−0.0981MPDay 2 + 0.381 • MPDay + 0.3413
Where :
C1

= Emission rate coefficient for CF4 dependant on the metal production of the cell, g CF4 / s · tonne
Al

C2= Emission rate coefficient for CF4 dependant on the metal production of the cell, dimensionlessC3= Emission rate coefficient for C2F6 dependant on metal production of the cell, g C2F6 / s · tonne
Al

C4= Emission rate coefficient for C2F6 dependant on the metal production of the cell, dimensionless.

MPDay= Average daily metal production per cell 11, for the cell technology, tonnes Al

Uncertainty levels when calculating PFCs from individual HVAE: The uncertainty range of each Tier 2b
methodology was estimated for SWPB, PFPBM and PFPBL technologies in order to facilitate the choice of one of
the two methods. These are shown in Table 4.16b.
TABLE 4.16B (NEW)UNCERTAINTY RANGEC (%) IN ESTIMATING PFC EMISSIONS FROM INDIVIDUAL HVAES (TIER 2B METHODS)
Technology

CF4 a,b

C2F6 a,b

Marks & Nunez
approachDion et al.
approachMarks & Nunez
approachDion et al.
approach

SWPB--36 / +51-

-42 / +68

PFPBL

-47 / +29

-36 / +51

-52 / +39

-42 / +68

PFPBM

-16 / +134

-33 / +61

-54 / +152

-24 / +13

Note:
Uncertainty ranges were evaluated for total emissions across multiple measurement campaigns and facilities (expert opinion). Overall,
11 measurement campaigns for PFPBM and 10 measurements campaigns with PFPBL or SWPB technology classes were used to estimate
the uncertainties related to CF4, while 5 measurement campaigns for PFPBM and 4 measurements campaigns with PFPBL or SWPB
technology classes were used to estimate the uncertainties related to C2F6 .
ab
Uncertainty ranges were calculated for HVAE emissions, where HVAEs were within the recommended HVAE duration (AED) limits ofthe (Dion et al. 2018a) method. It is possible that the uncertainty increases if the AED exceeds recommended limits when using the (Dionet al. 2018a) method, i.e. 1000 s and 150 s for CF4 and C2F6 estimations, respectively.

The uncertainty range calculated in Table 4.16B is based on a comparison with direct measurements and should not be compared to thereported Tier 2a uncertainty range from table 4.16 which compares variations of EF. For comparison, the calculated CF4 uncertainty
range for Tier 2a based on direct measurements is (-44% / + 388%) for legacy facilities and (-22% / + 256%) for modern facilities. The
calculated C2F6 uncertainty range for Tier 2a based on direct measurements is (-58% / + 8%) for legacy facilities and (-19% / +97 %) for
modern facilities.

cTier 3: PFC emission factors based on a facility specific relationship between
HVAE and LVAE performance and PFC emissions
Tier 3 methods are based on facility-specific coefficients or emission factors to estimate PFCs:

Day in Equation 4.27g is the average metal production per cell per day – it can be estimated from potline data or from theline amperage and average current efficiency of the potline. Care should be taken not to confuse this with the variable ‘MP’
– total metal production from the facility over the accounting period – used in other equations.

11 MP

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For HVAE emissions, Tier 3aHVAE and 3bHVAE coefficients characterize the relationship between facility HVAE
performance and measured PFC emissions from periodic or continuous measurements that are consistent withestablished measurement practices and latest industry protocols (US Environmental Protection Agency &International Aluminium Institute 2008).
For LVAE emissions, facility-specific Tier 3LVAE LVAE/HVAE emission ratios or LVAE emission factors can beestablished based on direct measurement of HVAE and LVAE for a period of time. There is ongoing work todevelop an updated measurement protocol for LVAE emissions to improve consistency and alignment acrossthe industry.
For cell start-up (CSU) emissions, Tier 3CSU production-based emission factors can be established based on direct
measurement of HVAE and LVAE emissions during the start-up of electrolysis cells; alternatively, direct
measurements can also be used to define Tier 3aHVAE or 3bHVAE and 3LVAE coefficients for emissions estimation(described above) specifically for cell start-up periods.
Tier 3DM is based on direct measurement at facilities, rather than estimation using on emission factors or
coefficients.

4.4.2.5

C HOICE OF ACTIVITY DATA

Production statistics should be available from every facility to enable use of Tier 1 methods for both CO2 and PFC
emissions. Uncertainty in the tonnages of aluminium produced is likely to be low in most countries. Given the
expected universal availability of production data, production capacity data should only be used as a check on
production statistics.
For CO2 emissions, all aluminium smelters collect data to support Tier 2 or Tier 3 methods. Søderberg smelters
collect anode paste consumption data while Prebake smelters record baked anode consumption. The Tier 2 andTier 3 methods use the same equation for calculation of CO2 emissions; however, the Tier 3 method uses facility
specific composition data for anode materials while the Tier 2 method uses industry average anode composition
data.
Good practice methods for PFC emissions resulting from high voltage anode effects (HVAE) require accurate
HVAE minutes per cell day data for all cell types. Annual statistics should be based on the production-weighted
average of monthly HVAE effect data. The Tier 2aHVAE and Tier 3aHVAE slope method utilizes overall performancestatistics for HVAE minutes per cell day and aluminium production data and Tier 3aHVAE overvoltage method
utilizes overall performance statistics for anode effect overvoltage and current efficiency. Similarly, Tier 2bHVAE
and Tier 3bHVAE utilises data on individual HVAE performance (anode effect duration) and line amperage or daily
average metal production at each facility.
Good practice methods for PFC emissions resulting from low voltage anode effects (LVAEs) require accurate
aluminium production data for Tier 1 (based on production-based, default emission factors) and Tier 3 (based on
production-based, facility-specific emission factors). For the alternative Tier 3 estimation based on the ratio of
LVAE/HVAE emissions, good practice methods for HVAE should be adopted as these are used in the calculationof LVAE emissions.
Good practice methods for PFC emissions from cell start-up (CSU) requires the same activity data described above
for HVAE and LVAE emissions (if using Tiers 2a, 2b, 3aHVAE or 3bHVAE and Tiers 1LVAE or 3LVAE), however witha data set specific to cell start-ups. Alternatively, if using Tier 3CSU facility-specific emission factors defined forcell start-ups, the only activity data required is the number of cell start-ups over the accounting period.
The direct measurement method for total PFCs (Tier 3DM) is not based on estimation and no activity data isrequired.
Individual aluminium companies or industry groups, national aluminium associations or the International
Aluminium Institute (IAI) should be consulted to ensure that the data are available and in a useable format for
inventory estimation.

4.4.2.6

C OMPLETENESS

Completeness for the aluminium production source category requires reporting of emissions of all GHGs (CO2,
CF4, and C2F6) from all sources (see Table 4.14) for all aluminium production in all smelters in a country. Primaryaluminium facilities will generally have good records of tonnes of aluminium produced throughout the entire timeseries covered by the inventory. In addition, carbon consumption data are typically available over the same period.
Process data on high voltage anode effects may be incomplete over the entire time series and measures may haveto be employed, such as those described in Section 4.4.2.7, Developing a Consistent Time Series, to calculate PFC

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Chapter 4: Metal Industry Emissions

emissions over some portions of the inventory period. Primary aluminium production also utilizes large amountof electricity and care should be exercised to avoid omissions of carbon dioxide associated with electricity input,
or, to avoid double counting of this carbon dioxide.
Furthermore, updates here in the 2019 Refinement provide significant advances in completeness, given the
inclusion of accounting for: (i) PFC emissions from LVAEs from primary aluminium production and (ii) PFC
emissions from cell start-ups (CSU), both of which were not previously accounted for in the 2006 IPCC Guidelines.
Despite greater completeness compared to the 2006 IPCC Guidelines, a higher level of uncertainty (imprecision)
overall is introduced in estimating total PFCs, given the higher uncertainties in accounting LVAE emissions.
Finally, care should be exercised to avoid double counting of PFCs from cell start-ups, if these are alreadyaccounted for in normal HVAE and LVAE emissions.

4.4.2.7

D EVELOPING A CONSISTENT TIME SERIES

General guidance on managing time-series consistency is available in Volume 1, Chapter 5; however, the following
provides guidance specific to aluminium production.

Time-series consistency for CO 2 emissions
Aluminium production statistics will typically be available for the entire history of the facility. Developing aconsistent time series for carbon dioxide emissions should not be a problem since most facilities historically havemeasured and recorded anode or paste consumption. Where historic anode or paste consumption data are missing,carbon dioxide emissions can be estimated from aluminium production utilizing the Tier 1 method.

Time-series consistency for High Voltage Anode Effect (HVAE) PFC emissions
A complete time series of PFC related activity data such as high voltage anode effect (HVAE) minutes per cell
day or overvoltage gives the best time series results. Because PFC emissions only became a major focus area inthe early 1990s for the global aluminium industry, some facilities may have limited information about the required
anode effect data to implement Tier 2 or Tier 3 PFC inventory practices over the entire time covered by theinventory. Substantial errors and discontinuities can be introduced by reverting to Tier 1 methods for PFC
emissions for years for which activity data are not available. The appropriateness of applying Tier 2 or Tier 3 PFC
emission factors back in time to a given facility and availability of detailed process data vary with the specificconditions. Generally, backcasting of Tier 2 or Tier 3 methods using splicing or surrogate data are preferred overuse of Tier 1 emission factors. Specifically, where only HVAE frequency data are available and HVAE duration
data are unavailable, it is good practice to splice or backcast PFC emissions per tonne aluminium based on HVAE
frequency data (implicitly assuming that anode effect durations did not change).
When going back in time using the Tier 1 or Tier 2a methodologies, it is important to take into consideration thechange in emission factors (for Tier 1) and slope coefficients for HVAEs (for Tier 2a). Accordingly, when using
these methods, it is generally good practice to use the default Tier 1 EFs and default Tier 2a slope coefficients inthe 2006 IPCC Guidelines prior to 2006. From 2006 through to the median year listed for each cell technology inTable 4.16c, default Tier 1 EFs and default Tier 2a slope coefficients can be interpolated from the 2006 IPCC
Guidelines and the 2019 Refinement. After that median year, the default Tier 1 EFs and default Tier 2a slope
coefficients from the 2019 Refinement should be used. As noted in section 4.4.1, the technology class in the 2006
IPCC Guidelines that corresponds to the PFPBL and PFPBM technology classes is CWPB. Because there is notechnology class in the 2006 IPCC Guidelines that corresponds well to the PFPBMW class, inventory compilers
should use the default EF for PFPBMW from the 2019 Refinement for the entire time series (i.e. from the time the
PFPBMW technology was first introduced into the country).
Inventory compilers switching from the Tier 3aHVAE overvoltage methodology to the Tier 3aHVAE slope model
should use both methods in parallel for a period of three years to evaluate the potential impact. However,publications demonstrated that the difference between both methods should be negligible with Tier 3 emission
factors (Dion et al. 2017; Marks & Bayliss 2012). If the difference between both methods is greater than 5 percent
over the transition period, then good practices would require contacting the International Aluminum Institute (IAI)
to be directed to expert advice to determine the optimal course of action for the best representativeness.
For inventory compilers switching from Tier 2a-3aHVAE (slope/overvoltage) to the Tier 2b-3bHVAE (non-linear)methodology to estimate HVAE emissions, it is consistent with good practices to adopt a similar protocol, i.e.
evaluate both methods in parallel for three years to evaluate impacts and if greater than 5 percent differences arenoted during the transition period, the IAI can be contacted for expert advice. Backcasting PFC emissions using
Tier 2b in 2019 and prior years is also possible, provided historical data on individual HVAE durations is stillavailable.
Currently many facilities are making PFC measurements that facilitate implementation of Tier 3 PFC inventory
methods. There are a number of issues that impact on whether Tier 3 PFC emission factors can be extrapolated to2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

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past inventory periods. Factors that should be considered include: (i) whether any technology upgrades have been
implemented at the facility, including significant amperage increase, new cell control system, or significant
changes in alumina feed control strategy affecting the frequency of HVAEs, (ii) whether there have been
substantial changes in work practices affecting the distribution of the HVAE durations, (iii)_whether any changes
in the calculation of underlying process data have occurred, and (iv) the quality of the measurements made toestablish the Tier 3 factor or coefficient. It is good practice to consult with representatives from the operating
facilities, either directly or through regional or international organizations representing the industry to develop thebest strategy for the specific group of operating locations included in the national inventory. Additional
information on splicing methods and details regarding constructing a time series for primary aluminium isavailable in The Aluminium Sector GHG Protocol (International Aluminium Institute 2006). Expert advice is alsoavailable from global and regional aluminium industry associations regarding greenhouse gas emissions andtypical industry emissions from aluminium production.
Table 4.16c has been provided to facilitate the choice of the correct HVAE emission factor (EF) for time consistent
inventories.
TABLE 4.16C (NEW)
TIME PERIOD OF MEASUREMENTS USED TO ESTABLISH UPDATED TIER 1 DEFAULT EFS AND TIER 2A DEFAULT SLOPE
COEFFICIENTSTechnology

Time Period

Use 2006 Guideline Defaults till 2006, then interpolate through to(Median Year)1

PFPBL

2013-2014

2013

PFPBM

2013-2016

2013

PFPBMW

2008-2012

Use 2019 Refinement Tier 1 EF for entire time series2

SWPB

2004-2015

2008

VSS

2003-2016

2007

HSS

2004-20122007

For each cell technology, the transition point is dependent on the time period when facility measurements were obtained. Here the medianyear for measurements is recommended as the transition point to use updated default EFs and coefficients from the 2019 Refinement.
1

2

For PFPBMW technology, median year is 2011, however use of updated Tier 1 EF is recommended for the entire time series.

Time-series consistency for Low Voltage Anode Effect (LVAE) PFC emissions
Low voltage anode effects (LVAEs) became a concern for the aluminium industry in the early 2010s, due to anincrease number of cell technologies with higher amperage and additional anodes (Chen et al. 2013; Wong &Marks 2013; Zarouni et al. 2013; Dando et al. 2015; Wong et al. 2015; International Aluminium Institute 2018).
Actual data indicates that these PFC emissions are greater for specific cell technologies, usually with cell amperage
higher than 350kA. Therefore, inventory compilers should backcast the LVAE PFC emissions, for national
inventories, by using the respective Tier 1 coefficient specific to each category back to 2006. Since 2006, theglobal aluminium industry has undergone changes in technology and operating conditions that make LVAE
emissions much more prevalent 12; these changes have occurred not only through uptake of newer technologies(e.g. PFPBL to PFPBM) but also during upgrades within the same technology in order to maximise productivity
and reduce energy use (Coursol et al. 2011, Kalban et al. 2013, Tarcy et al. 2011). The relative insignificance ofemissions from LVAE before 2006 is also supported by (i) the lack of industry reports detecting LVAE emissions
in PFC measurements prior to 2006, (ii) the very high frequencies of HVAEs (and hence high HVAE emissions)prior to 2006 outweighing any small contributions of LVAE emissions, and (iii) the agreement in global top-down
and bottom-up industry estimates of total PFCs prior to 2002 (Wong et al., 2015). Hence, it is not recommended
to backcast LVAE PFC emissions prior to 2006.

12 The fundamental factors that make LVAE emissions more prevalent in today’s current smelting technologies were lesssignificant prior to the 2006 IPCC Guidelines (expert judgement). These factors include: higher anode current density (Amps
per cm2 anode surface) to maximise cell productivity, lower anode-cathode distance to minimise cell voltage and hence
energy use, larger anode dimensions which reduced the volume of liquid electrolyte to dissolve alumina, greater demand on
transporting alumina to all anodes per point feeder (for PFPB technologies), and longer cells with significantly more anodes
increasing the risk of localised issues in cells. These trends in the industry have occurred not only from the uptake of newtechnologies (e.g. from PFPBL to high amperage PFPBM), but also through incremental upgrades within the same technology
class (e.g. modernising existing PFPBL technology) to enable greater metal productivity and reduced energy use. Examples
of upgrades within the same technology include Coursol et al. 2011, Kalban et al. 2013, Tarcy et al. 2011, many of which
also led to a reduction in HVAE emissions, making LVAE emissions more significant in comparison.

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If Tier 3 coefficients are available, it is good practice to use these coefficients for past inventory periods insteadof using Tier 1 coefficients. There are several issues that impact the uncertainty of Tier 3 PFC emission factors
when extrapolated to past inventory periods. The factors presented in the previous section on high voltage anodeeffects are also applicable when estimating the possibility of extrapolating LVAE estimations outside of themeasured EF period. It is particularly important to consider any significant change in the alumina feeding strategy
as it can significantly impact the LVAE emission coefficient. Finally, the study performed by (Dion et al. 2018b)
highlighted the importance of considering numerous facilities when estimating LVAE emissions using Tier 1
emission factors. Inventory compilers should therefore be aware of the limitations associated with the Tier 1
coefficients included in this guidance when applying it to a limited number of smelters, or when used for a single
facility. This is driven by the high uncertainty of LVAE PFC emissions from individual smelters and the possible
variability of these emissions related to different control process parameters between the different facilities.
Table 4.16d has been provided to facilitate the choice of the correct LVAE emission factor (EF) for time consistent
inventories.
TABLE 4.16D (NEW)SUMMARY OF WHICH GUIDELINES TO REFER TO, FOR TIME CONSISTENT PFC INVENTORIES
For
estimation of:Time frame
Prior to 2006

2006 to 20192020 and beyond

HVAE
emissions

Refer to 2006 IPCC
Guidelines for methodology
and adequate EF.

Refer to Table 4.16c from the2019 Refinements to select anappropriate year for the EF
transition based on the cell
technologies.

Refer to 2019 Refinement formethodology and adequate
EF.

LVAE
emissions

LVAE considered immaterial
due to the high levels of
HVAE from smelters1 during
this period1. It is good practice
not to report LVAE.

Refer to 2019 Refinement formethodology and adequate
EF.

Refer to 2019 Refinement formethodology and adequate
EF.

(International Aluminium Institute 2018). Refer to footnote 1 on the previous page, for factors that have led to LVAE emissions
becoming more prevalent in the aluminium industry following the time of the 2006 IPCC Guidelines.

1

4.4.3

Uncertainty assessment for primary aluminium
production

There are major differences in the uncertainty for PFC emissions depending on the choice of Tier 1, Tier 2, or Tier
3 methods. The differences in uncertainty resulting from choice of method for carbon dioxide emissions are muchsmaller than for PFC emissions. There is no basis for country or regional differences in emissions resulting fromaluminium production other than the differences that result from the specific type of production technologies andwork practices in use in the country or region. These differences are reflected in the calculation methodologies
described above.

4.4.3.1

E MISSION FACTOR UNCERTAINTIES

Uncertainties for CO 2 emissions
The uncertainty in the emission factors for calculating carbon dioxide emissions from carbon anode or paste
consumption should be less than ±5 percent for both the Tier 2 and Tier 3 methods, and less than ±10 percent for
the Tier 1 method. The reactions leading to carbon dioxide emissions are well understood and the emissions arevery directly connected to the tonnes of aluminium produced through the fundamental electrochemical equations
for alumina reduction at a carbon anode and oxidation from thermal processes. Both of these fundamental
processes producing carbon dioxide are included in process parameters routinely monitored at the production
facilities, the net carbon consumed and/or paste consumption. The main source of uncertainty is in the net carbon
consumed for Prebake technologies and paste consumption for Søderberg cells. These factors are both carefully
monitored and are important factors in the economic performance of a facility. Improvements in accuracy of carbon
dioxide emissions inventories can be achieved by moving from Tier 1 to Tier 2 methods because there is a rangeof performance of reduction facilities in the consumption of carbon anode materials. Less significant

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improvements in accuracy can be expected in choosing the Tier 3 method over the Tier 2 method. This is because
the major factors in the calculation are the net anode carbon consumed or paste consumption and the productionof aluminium. The uncertainty of both these components of the calculation equation is low, 2 to 5 percent, andthese uncertainties dominate the overall calculation of carbon dioxide emissions in the Tier 2 and Tier 3 methods.
Facility specific data are used in both Tier 2 and Tier 3 calculations for these parameters. The Tier 3 method refines
the calculation to use actual composition of the carbon anode materials. While there can be considerable variability
in the minor components of the anode materials this variability does not contribute significantly to the overallcalculation of carbon dioxide emissions.

Uncertainties for PFC emissions
In considering changes in uncertainty in PFC emissions inventory when moving from Tier 1 to Tier 2 and Tier 3
methods, there are major reductions in uncertainty when choosing the Tier 2 or Tier 3 methods over the Tier 1
method.
For HVAE emissions, the high level of uncertainty in the Tier 1 method reflects the significant variability in HVAE
performance from one facility to another within the same technology class. The Tier 1 method is based on using asingle default coefficient for all operators by technology type. Since there can be variations in anode effectperformance (frequency and duration) by factors of 10 among operators using the same technology (IAI, 2005c),
use of the Tier 1 method can result in uncertainties of the same magnitude. There is less impact on uncertainty
levels in choosing the Tier 3 methods (3aHVAE and 3bHVAE) over the Tier 2 methods (2a and 2b) for estimating
HVAE. When using the Tier 2a or 2b methods , the level of uncertainty reduction depends on the cell technology
type. For example, the uncertainty for Tier 2a industry slope coefficients for individual facilities ranges from -27
to +32 percent for PFPBM, to -53 to +130 percent for VSS. Compared to Tier 2a, the Tier 2 method provides
significantly lower levels of uncertainty (roughly 3-5 times less, expert opinion) for individual facilities in termsof estimated PFC emissions; however again, the level of uncertainty depends on technology type.
Both Tier 2 (2a and 2b) and Tier 3 (3aHVAE and 3bHVAE) methods are based on direct PFC measurements that
establish a relationship between HVAE performance and PFC specific emissions. The Tier 2 methods use average
equation coefficients by technology while the Tier 3aHVAE and 3bHVAE methods uses facility-specific coefficients
based on direct PFC measurements made at the facility. The lowest uncertainty for PFC emissions calculations
from HVAE is from the use of the Tier 3bHVAE method, followed by the Tier 3aHVAE method. However, to achieve
this lower uncertainty in Tier 3 PFC calculations it is important to use good practices in making facility specific
PFC measurements. These measurement good practices have been established and documented in a protocol
available globally (US Environmental Protection Agency & International Aluminium Institute 2008); it is goodpractice to check for updates to these protocols. When properly established these Tier 3 coefficients will have an
uncertainty of +/-15 percent at the time the coefficients are measured.
For LVAE emissions, there is a high level of uncertainty associated with emission estimates using Tier 1. The Tier
3LVAE method has a much lower uncertainty than Tier 1 as it is facility specific and based on a period of direct
measurement at the site. LVAE is a relatively new discovery in the aluminium industry and as such, researchcontinues on the best predictors and models to use to estimate LVAE emissions. There is also high variability
observed between different facilities which results in large uncertainty ranges for the measured data that underpins
the emissions factors. A measurement protocol for LVAE measurements to support the Tier 3LVAE methodology
is still under development and it is expected that such industry guidance to align measurement procedures andprocesses will improve consistency across the industry. Furthermore, considering the typically low concentrationsof LVAE emissions and the detection limits of measuring instruments, it is expected that the uncertainty of theTier 3LVAE method for LVAE emissions will be larger than that fore Tier 3 methods (3aHVAE and 3bHVAE) to estimate
HVAE emissions. Finally, while Tier 3LVAE provides the lower uncertainty for LVAE estimations than Tier 1, thelowest overall uncertainty for total PFC emissions is from the Tier 3DM method, i.e. direct measurement of total
PFCs.
For CSU emissions, there is no specific methodology at the Tier 1 level, since CSU emissions are implicitly
included in Tier 1 methods for estimating HVAE and LVAE emissions. However, given the wide variation in cell
technologies and start-up operating practices from one facility to another, a higher level of uncertainty is expectedat Tier 1 (as discussed previously for HVAE and LVAE emissions). If CSU emissions are accounted for separately,use of the Tier 2b method is likely to provide lower uncertainties compared to the Tier 2a method (with standard
slope coefficients, which may overestimate HVAE emissions). Similarly, when facility-specific at Tier 3
coefficients are available, use of the Tier 3bHVAE method is expected to provide lower levels of uncertainty than
the Tier 3aHVAE method. However, lowest uncertainties can be obtained through use of one of the following: (a)Tier 3aHVAE or Tier 3bHVAE emission coefficients for HVAE emissions, combined with Tier 3LVAE coefficientsdetermined specifically for CSU periods, or (b) use of Tier 3CSU total emission factors determined specifically for
CSU periods.

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Finally, the Tier 3DM direct measurement method, following industry best practices, provides the lowest of
uncertainty level for all accounting methods for all PFC emissions (HVAE, LVAE and CSU), since the only
sources of uncertainty is related to sampling procedures and measurement error.

4.4.3.2

A CTIVITY DATA UNCERTAINTIESThere is very little uncertainty in the data for the annual production of aluminium, less than 1 percent. The
uncertainty in recording carbon consumption as baked anode consumption or coke and paste consumption isestimated to be only slightly higher than for aluminium production, less than 2 percent. For HVAE PFC emissions,the other component of calculated facility specific emissions using Tier 2a or Tier 3aHVAE methods is the overall
anode effect activity data, i.e.: anode effect minutes (AEM) per cell day for the slope method, or anode effectovervoltage (AEO) for overvoltage method. These parameters are typically logged by the process control systemas part of the operations of nearly all aluminium production facilities and the uncertainties in these data are low. It
also applies to the Tier 2b and 3bHVAE approach where potline current and AED for individual HVAEs are precisely
monitored by the cell control system; the only exception are cases where this individual AED data is automaticallyconsolidated into overall anode effect performance statistics by the facility’s software on a daily basis, or fordifferent periods, which prevents the use of this method. Further activity data required for Tier 2b or 3bHVAE method(Dion et al. approach) is the average daily metal production per cell, which has very little uncertainty in the data,
less than 5 percent. For estimation of CSU emissions using the Tier 3CSU method, there is very little uncertainty on
the recorded number of cell start-ups (NCSU) per accounting period, less than 2 percent.

4.4.4

4.4.4.1

Quality Assurance/Quality Control (QA/QC)
Reporting and Documentation for primaryaluminium production
Q UALITY A SSURANCE /Q UALITY C ONTROL (QA/QC)

It is good practice at all primary aluminium production facilities to maintain records of all of the necessary activity
data to support calculations of emissions factors as suggested in these guidelines. These records will include
production of aluminium, anode effect performance and consumption of carbon materials used in either Prebake
or Søderberg cells. In addition, the International Aluminium Institute maintains global summaries of aggregatedactivity data for these same parameters and regional data are available from regional aluminium associations. It isgood practice to aggregate emissions estimates from each smelter to estimate total national emissions. However,
if smelter-level production data are unavailable, smelter capacity data may be used along with aggregate national
production to estimate smelter production.
It is good practice to verify facility CO2 emission factors per tonne aluminium by comparison with the expected
range of variation that would be predicted from the variation noted in Tables 4.10 and 4.11 for carbon dioxide
specific emissions. Also, the underlying equation coefficients used for calculating PFC emission factors per tonne
aluminium should be compared with those noted. It is suggested that any inventory value outside the 95 percent
confidence range of the data population variance be confirmed with the data source.
Use of standard measurement methods improves the consistency of the resulting data and knowledge of thestatistical properties of the data. For HVAE emissions from primary aluminium, the ‘EPA/IAI Protocol for
Measurement of Tetrafluoromethane (CF4) and Hexafluoroethane (C2F6) Emissions from Primary Aluminum
Production’ is the internationally recognized standard (US Environmental Protection Agency & International
Aluminium Institute 2008). Significant differences between calculated Tier 3aHVAE or 3bHVAE coefficients basedon PFC measurements and the respective industry average Tier 2a or 2b coefficients for similar reduction
technology should elicit further review and checks on calculations. Large differences should be explained anddocumented. The International Aluminium Institute (IAI) collects anode effect performance data from a numberof smelters and can be consulted for assistance in identifying outlier data. . In addition, an up-to-date database of
PFC measurements is also maintained by IAI and should be consulted when assessing the appropriateness ofreported data. For LVAE emissions measurements which are relatively new and as yet, not widely measured,
protocols are under development to improve consistency and alignment across the industry. Industry associations
such as the IAI can be consulted for the latest developments.
Inter-annual changes in emissions of carbon dioxide per tonne aluminium should not exceed +/-10 percent basedon the consistency of the underlying processes that produce carbon dioxide. In contrast, inter-annual changes in2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

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Volume 3: Industrial Processes and Product Useemissions of PFCs 13 per tonne of aluminium may change by values of up to +/- 100 percent. Increases in PFC
specific emissions can result from process instability. Increases in anode effect frequency and duration can be theresult of factors such as unanticipated power interruptions, changes in sources of alumina feed materials, cell
operational problems, and increases in potline amperage to increase aluminium production. Decreases in PFC
specific emissions can result from decreases in anode effect frequency and duration due to changes in the computer
algorithms used in cell process control, upgrades in cell technology such as the installation of point feeders,
improved work practices and better control of raw materials.

4.4.4.2

R EPORTING AND DOCUMENTATION

It is good practice to document and archive all information required to produce the national emissions inventory
estimates as outlined in Volume 1, Chapter 6, Quality Assurance and Quality Control, Internal Documentation andArchiving. Some examples of specific documentation and reporting relevant to this source category are provided
below.
It is not practical to include all documentation in the national inventory report. However, the inventory should
include summaries of methods used and references to source data such that the reported emissions estimates aretransparent and steps in their calculation may be retraced. To improve transparency, it is good practice to reportemissions for PFCs from aluminium production separately from other source categories. Additionally, it is goodpractice that CF4 and C2F6 emissions are reported separately on a mass basis.
The supporting information necessary to ensure transparency in reported emissions estimates is shown in Table
4.17, good practice Reporting Information for PFC Emissions from Aluminium Production by Tier, below.
Much of the production and process data are considered proprietary by operators, especially where there is only
one smelter in a country. It is good practice to exercise appropriate techniques, including aggregation of data, toensure protection of confidential data.

13 Reference to PFCs from this section applies to both HVAE and LVAE emissions.

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TABLE 4.17 (UPDATED)GOOD PRACTICE REPORTING INFORMATION FOR CALCULATING CO2 AND PFC EMISSIONS FROM ALUMINIUM PRODUCTIONBY TIER

Data

Tier 1

Tier 2Tier 3

2a

2b

3a

3b

HVAE

HVAE

HVAE

HVAE

3LVAE

3CSU

3DM

PFCs (CF4, C2F6 reported separately on mass basis)
Annual national production (by technology)

X

Annual production by smelter (by technology)

X

X

Daily average production by smelter (bytechnology)1X

Annual current efficiency by smelter (bytechnology)2

X
X

X

Anode Effect Minutes per cell-day

X

X

Anode Effect Overvoltage (mV)X

Anode Effect Duration for individual HVAE bysmelter3

X

X

Line amperage (kA) during individual HVAE bysmelter3,4

X

X

Number of cell start-ups by smelter
Default technology emission coefficients

X
X

Technology specific emission coefficients linked to
HVAE performance

X

X

Facility specific emission coefficients linked to
HVAE performance

X

X

Facility specific emission coefficients linked to
LVAE performance

X

Facility specific emission coefficients linked to cellstart-up

X

Facility specific emission mass by direct
measurement
Supporting documentation

X
X

X

X

X

X

X

X

X

CO2
Annual national production (by Prebake or
Søderberg technology)

X

Annual production by smelter (by Prebake or
Søderberg technology)

X

X

Net anode consumption for Prebake cells or paste
consumption for Søderberg cells

X

X

Carbon material impurity levels and carbon dust for
Søderberg cells

X

Notes:
1

Daily average production data is only used in the Tier 2b/3b Dion et al. method, but not required for the Marks & Nunez method.

2

Current efficiency data used only in the Tier 3a Overvoltage Method, but not required for Tier 3a Slope Method.

Given the total number of HVAEs that occur in a facility annually, it is not practical to report to individual anode effect data for all
HVAEs by smelter in the national inventory report. However, the inventory should include summaries of methods used and references tosource data such that the reported emissions estimates are transparent and steps in their calculation may be retraced.
34Line current data are only used in the Tier 2b/3b Marks & Nunez method, but not required for the Dion et al. method.

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4.4.5

Methodological issues for alumina production

This guidance does not consider any new methodological issues associated with GHG emission inventories for the
production of alumina from the conventional Bayer process. Emissions from the Bayer process are covered byexisting guidance for fossil fuel combustion (Volume 2, Chapter 2) and for lime production (Volume 3, Section
2.3).
Methodological issues for alumina production from Bayer-sintering parallel (BSP), Bayer-sintering sequential(BSS) and Nepheline processing (NP) only are considered in this section (see Figure 4.12b). In 2017, only around
3 percent of alumina was produced globally via the Bayer-sintering process and around 1 percent via the Nepheline
processing mainly in 3 countries – Russia, Kazakhstan and China.

4.4.5.1

A LTERNATIVE ALUMINA REFINING PROCESSESBAYER-SINTERING PROCESSThe Bayer-sintering process is an alternative process to the more conventional Bayer process and is used when thebauxite feed has a high silica content making processing by the conventional Bayer process uneconomical due tohigh soda and alumina loss. The Bayer-sinter process involves a sintering stage (either with soda or with soda andlimestone) that produces a solid sodium aluminate sinter which is then leached to form the sodium aluminate liquor(green liquor).
The process to produce green liquor is an alternative process to bauxite digestion which takes place in theconventional Bayer process. Green liquors from both Bayer and sintering branches of the process are cooled andheld in precipitator vessels which results in the precipitation of alumina hydrate that is filtered and washed.
The alumina hydrate is then passed through a rotary or stationary calciner at 1100°C to drive off the chemicallycombined water. The result is a white powder, pure calcined or ‘metallurgical’ grade alumina (Al2O3), which isthe basic raw material for primary aluminium production.
Depending on bauxite quality there two variations of the Bayer-sintering process: parallel and sequential. In thecase of the parallel process (BSP), a proportion of the bauxite feed (up to 20-30 percent) is processed in thesintering branch and the rest is effectively processed by the conventional Bayer process (Figure 4.12b). In the caseof sequential process (BSS), all bauxite is Bayer digested and red mud is mixed with soda and limestone and fed
to the sintering operation to recover soda and alumina from it.
The main sources of the greenhouse gases emissions of CO2, N2O and CH4 from the Bayer-sintering process arelisted below, of which, the sintering step is the main focus of this section:
Sintering (fuel combustion 14 and carbonates decomposition 15);
Power and heat production facilities (fuel combustion1);
Alumina hydrate calcination (fuel combustion1);
Lime calcination (fuel combustion and carbonates decomposition 16).

•
•
•
•

14 Calculation of GHG emissions shall be done in accordance to Volume 2 Energy, Chapter 2 Stationary Combustion for FuelBurning.

15 Emissions from carbonate decomposition shall be calculated in accordance to Section 4.4.5.2 of current chapter.
16 Calculation of GHG emissions shall be done in accordance to Volume 3 Industrial Processes and Product Use, Chapter 2

Mineral Industry Emissions, Section 2.3 Lime Production.

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Figure 4.12b (New)

Alumina production processes

Lime calcination

Bayer
processing

CO2

Red mud to disposal

CaO

Hydrochemical processes(digestion, desilication, thickening,
precipitation, evaporation, red mud washing)

NaOH
BauxiteLime calcination

CO2

Al2O3

Aluminahydratecalcination

Al2O3

Red mud to disposal

CaO

Bayersinteringparallelprocessing

Aluminahydratecalcination

Hydrochemical processes(digestion, desilication, thickening,
precipitation, evaporation, red mud washing)

NaOH
BauxiteNa2CO3 slurry
CaCO3

CO2

Hydrochemical
processes

Sintering

Na2CO3
BauxiteRed mud to disposal

Lime calcination
CaO

Bayersintering
sequential
processing

NaOH
BauxiteCO2

Hydrochemical processes(digestion, desilication, thickening,
precipitation, evaporation, red mud washing)Aluminahydratecalcination

Red mud
CO2
CaCO3

Sintering

Na2CO3Al2O3Hydrochemical
processes
Red mud to disposal

CO2
CO2Nepheline

Nepheline
processing

CaCO3

NaAl(OH)4

Aluminahydratecalcination

Al2O3(digestion, desilication,
thickening, precipitation,
evaporation, belite mud
washing)

CaO

Na2CO3

Na2CO3

Hydrochemical
processes

Sinteringkiln**

Lime calcination*

Carbonization**

CO2

Belite mud to cement
production and to disposal* Calculated in accordance to Volume 3 Industrial Processes and Product Use, Chapter 2 Mineral industry emissions, Section 2.3 Lime
production.
** Calculated in accordance to Section 4.4.5.2 of the current chapter.

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NEPHELINE PROCESSThe Nepheline process (NP) is another alternative route for alumina production (<1 percent of global production 17
in 2017), which uses nepheline as the raw material as opposed to bauxite in the conventional Bayer process.
Nepheline ore is a sodium and potassium containing aluminosilcate that contains more silica than alumina. In orderto make silica insoluble at the leaching process, it is combined with lime forming 2CaO • SiO2 (belite) using thesintering process. The belite mud may be used in the cement production whereas sodium and potassium streams
may be used to produce soda ash and potash resulting in complex processing of nepheline raw material.
The main steps in the process are (refer to Figure 4.12b): crushing and milling of nepheline with limestone andrecycled soda liquor forming the raw mix; and sintering of the raw mix (at about 1300°C) in rotary kilns where
calcium carbonate is decomposed and the following reaction between calcium oxide and nepheline takes place,
forming CO2:

4CaCO3 + ( Na, K )2 O • Al2O3 • 2 SiO2 → 2 ( Na, K ) O • AlO2 + 2 ( 2CaO, SiO2 ) + 4CO2
The nepheline sinter is leached with the dissolution of alkali aluminate. The sinter residue is separated andtransported to be used in cement production and the aluminate liquor is passed on for desilication to remove
partially dissolved silica from the liquor. Then, alumina hydrate is obtained from the green liquor partly bydecomposition and partly by carbonisation. Carbonisation captures CO2 in the process (Figure 4.12b).
The main sources of greenhouse gases emissions from the nepheline process are similar to the Bayer-sintering
process. To avoid double counting CO2 emissions related to by-products produced alongside alumina (i.e. belite
mud for cement, soda ash, potash), shall be considered only in relation to the raw materials required for thealuminium production process.

OTHER GHG SOURCES AND CAPTURE
CO2 and CH4 are also produced during other sub-processes that are implemented or may be implemented at allalumina refineries but the emissions from such processes are currently considered to be negligible and not a main
source of GHG emissions (<1 percent, expert judgement).
Examples of such sub-processes include: flue gas desulphurization, acid cleaning of process equipment, organiccarbon in bauxite, liquor burning, etc.
There are also a number of CO2 capture pathways to consider:•••

Carbonisation;
CO2 absorption through use of bauxite residue for flue gas desulphurization;
CO2 absorption through use of water collected from bauxite/nepheline storage residue area.

As noted throughout Volume 3 on Industrial Processes and Product Use (IPPU), the emission estimation
methodologies outlined in this Chapter consider only process-related emissions and do not consider energy-related
emissions. Inventory compilers should ensure that energy-related emissions are accounted for in the Energy Sector
and that there is no double-counting of emissions between the Energy and IPPU Sectors. For example, thecalculation of CO2 emissions from fuel consumed in lime calcination, sintering, alumina hydrate calcination andelectricity and heat production at a facility’s own boilers, CHP or power plants should be considered using theguidance related to the combustion of fossil fuels.

There is only a single alumina refinery that uses this technology (Russia) and estimate is based on its annual
production as a proportion of total global alumina production.

17

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CO 2 capture from Carbonisation in nepheline process

The main reactions of CO2 capture by during the Carbonisation sub-process are:Stage 1

NaAl ( OH )4 + CO2   → Al ( OH )3↓+ NaHCO3
Stage 2

2 NaAl ( OH )4 + 2 NaHCO3   → Na2O • Al2O3 • 2CO2 • 4 H 2O↓+ 2 NaOH

2 NaOH + CO2 → Na2CO3 + H 2OPart of CO2 after Sintering is passed through gas treatment facilities to remove particles and other harmful
components and then forwarded to carbonisators, where the carbonisation reaction proceeds step by step. This isdone in a two-stage process.

CO 2 absorption through use of circulating water collected from bauxite/nepheline
storage residue area

If a refinery uses circulating water collected from bauxite/nepheline storage residue area, which contains a lot of
sodium alkaline to treat flue gas to remove particles, SO2 and other acid gases it should be assumed that the
scrubbing system will also remove some CO2 in the flue gas. The efficiency of CO2 capture is very dependent on
concentration of sodium alkaline in circulating water and type of scrubbing technology. If there is a lack of direct
measurement data on CO2/CO in flue gas where such scrubbing system is used, it is not recommended that CO2
removal be considered in CO2 calculations.

CO 2 absorption through bauxite residue neutralization

Carbonation of bauxite residue (red mud) can be carried out to utilize the capacity of this waste to capture CO2
and in turn, the capacity of CO2 to neutralize the highly alkaline red mud. The absorption of CO2 is rapid and canbe efficient if there is good contact between the residue and the CO2. For high concentration CO2 streams (90percent or more) the reaction can be virtually 100 percent with a few seconds contact. Total alkalinity of red mud
drops drastically with the added CO2 recorded as an increase in bicarbonate alkalinity.
For lower concentrations of CO2 such as flue gas where concentrations may be 12-15 percent, the reaction
efficiency will be reduced. If CO2 removal data is not available for bauxite residue contacted with gases containing
less than 50 percent CO2, then it is recommended that reaction efficiency of 35 percent be assumed by default.
CO2 absorption can be estimated by multiplying the quantity of CO2 injected into the process multiplied by themeasured or assumed reaction efficiency.
Measurement of the increase in bicarbonate in the residue can also be used as a better measure of the amount of
CO2 actually absorbed in the neutralization process.

4.4.5.2

C HOICE OF METHOD FOR ALUMINA PRODUCTION

The decision tree in Figure 4.12c describes good practice in choosing the most appropriate method based onnational circumstances.
In the Tier 1 method, emissions are estimated using alumina production data and national or default emission
factors for the relevant technologies. The estimation of emissions directly from alumina production, without
process specific information about raw materials and technology, is subject to high levels of uncertainty. This isbecause emissions from carbonates decomposition in the sintering and/or lime calcination processes can varysignificantly.
Tier 2 implements method from Tier 1 but country-specific emission factors should be applied.

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The Tier 3 approach relies on plant specific data. Tier 3 methods should also include a correction for emissions ofdust. Tier 3 also includes a correction addition for emissions associated with dust not recycled to the kiln. Any
uncalcined dust not recycled to the kiln should be subtracted from the total emissions estimate.
Should CO2 capture technology be installed and used at a plant, it is good practice to deduct the CO2 captured ina higher tier emissions calculation (Tier 3). The default assumption is that there is no CO2 capture and storage(CCS) taking place. Any methodology taking into account CO2 capture should consider that CO2 emissions
captured in the process may be both fuel combustion and process-related. In cases where combustion and process
emissions are to be reported separately, e.g. for alumina production, inventory compilers should ensure that thesame quantities of CO2 are not double counted. In these cases, the total amount of CO2 captured should preferably
be reported in the corresponding energy combustion and IPPU source categories in proportion to the amounts of
CO2 generated in these source categories. For additional information on CO2 capture and storage refer to Volume
3, Section 1.2.2 (under Industrial Processes and Product Use) and Volume 2, Section 2.3.4 (Under Energy).

TIER 1 METHOD FOR SINTERINGThe Tier 1 method for lime production emissions is described in (Volume 3, Section 2.3.1.1). To avoid double
counting, before applying this method it is essential to check whether lime production data from alumina plants isalready considered in the inventory for lime production. If the lime production process at alumina plants has notbeen, included, the emissions associated with this process shall be considered as source related to alumina
production. To attribute lime production emissions specifically to alumina production, it is necessary to gather
data on how much of the national lime production occurs at alumina plants.
The Tier 1 method for the sintering process (including BSP, BSS and NP alumina production processes) is basedon default emission factors, but requires country specific activity data on production mass produced by BSS, BSP
and NP processes. If the Bayer-sinter (BS) process is used, the GHG emissions from the sintering are dependent
on the quality of bauxite and the silica content of the bauxite. High silica content, low content of Al2O3 in ore leads
to use of high carbonate content which results in greater GHG emissions. In case of Nepheline processing (NP),
GHG emissions from the sintering are dependant on the Al2O3 content of the nepheline ore.
If detailed and complete data (including mass and composition) for the carbonates consumed in the sintering andlime production processes are not available, it is good practice to use aggregated national alumina production data,
based on the technology applied, raw material and data on the proportion of Bayer and Bayer-sintering, expressedas an emission factor in the following Equation 4.27g:

EQUATION 4.27G (NEW)
TIER 1: SINTERING PROCESS EMISSIONS BASED ON ALUMINA PRODUCTION DATA

CO2 Emissions= M BS _ Al2O3 • S BS • EFBS _ Sint + M NP _ Al O3 • S NP • EFNP_Sint + M Lime • EFLime
2

Where:
CO2 Emissions = emissions of CO2 from sintering production, tonnes

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MBS_Al2O3= mass of alumina produced by BSP and BSS processes, tonnes

MNP_Al2O3= mass of alumina produced by NP processes, tonnes

MLime= mass of lime produced, tonnes.

SBS= mass fraction of alumina produced by sintering process (BSP and BSS). The parametercan be varied from 0 to 1, where 1 is related to 100 percent of alumina produced bysintering process. If there is no information about country specific mass fraction, 1 shallbe used with assumption that 100 percent of alumina produced by sintering process.

SNP= mass fraction of alumina produced by sintering process. The parameter equals 1,
because 100 percent of alumina in the NP process is produced by sintering process.

EFBS_Sint= default emission factor for sintering BSP and BSS processes, tonnes CO2/tonne alumina(see discussion under Section 4.4.5.3 Choice of Emission Factors), which is not corrected
for dust.

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EFNP_Sint= default emission factor for sintering NP process, tonnes CO2/tonne alumina (seediscussion under Section 4.4.5.3 Choice of Emission Factors), which is not corrected for
dust.

EFLime= default emission factor for lime production, tonnes CO2/tonne lime (Volume 3, Section
2.3.1.2)

The Tier 1 approach is based on the following assumptions about the alumina production and sintering process:
•
•
•
•
•
•
•
•

The mass fraction of alumina produced by sintering process (rather than the leaching process) isstable over time;
In case of alumina production from the nepheline ore, 100 percent of alumina is produced with thesintering process;
Plants are generally able to control the CaCO3 content of the raw material inputs and output ofsintering process within close tolerances;
The CaCO3 content of the raw materials inputs from a given plant tends not to change significantly
over time;
The main source of the CaO for most plants is CaCO3 and, at least at the plant-specific level, any
major non-carbonated sources of CaO are readily quantified (see Section 4.4.5.3 below);
A 100 percent (or very close to it) calcination factor is achieved for the carbonate inputs for sintering
output, including (commonly to a lesser degree) material lost to the system as non-recycled dust; andDust collectors at plants capture essentially all of the dust;
The capture of CO2 cannot be quantified and assumed to be zero.

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Figure 4.12c (New)

Decision tree for estimation of CO 2 emissions from alumina production

Start

Is alumina producedin the country?

No

There are no process-related emissions
from alumina production. Report emissions
as "not occurring".
Box 5: Emissions Not OccurringYes

Is alumina
Being produced with onsite
lime calcination and BSP,
BSS or NP?

No

The emissions shall be calculated inaccordance with Volume 2 Energy,
Chapter 2 Stationary combustion.
Box 4: Energy related emissions

Yes

Are detailed
site-specific data available
for carbonate inputs used insintering and lime
calcination?

Yes

No

Collect plant-specific activity data on
carbonates consumed (their chemicalcomposition and calcination achieved) andrelevant emission factors as basis for Tier 3
method. Where analysis of carbonates isdone on a periodic basis, alumina
production data may be used as a proxy.
Correct for dust.
Box 3: Tier 3

Is this a key category1?

Yes

Use country-specific EF and method inTier 1
Box 2: Tier 2

No
Use fraction for quantity of lime producedby type and apply respective default
emission factors.
Calculate emissions based on national
alumina production statistics for particulartechnology and raw material data.
Box 1: Tier 1
Note:
1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for
discussion of key categories and use of decision trees.

TIER 2 METHOD FOR SINTERINGThe Tier 2 method is a country specific method. This uses the same approach to Tier 1 in accordance with Equation
4.27g, but with regional or country specific emissions factors for calculation of CO2 from sintering, instead ofdefault emission factors.

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TIER 3 METHOD FOR SINTERING: USE OF CARBONATE INPUT DATA
Where national level data for lime production at alumina refineries are available on the types of lime produced, it
is good practice to estimate emissions using a Tier 3 approach described in of Chapter 2, Section 2.
For sintering processes, CO2 emissions are calculated using a mass balance approach that considers the carbonatesand carbon content of input and output materials. Carbonates of input materials are destroyed due to hightemperatures in sintering kilns. The Tier 3 method uses actual concentrations of impurities.
Tier 3 is based on the collection of disaggregated data on the types (compositions) and quantities of carbonates
consumed in the sintering process at a particular plant, as well as the respective emission factors of the carbonates
consumed. Emissions are then calculated using Equation 4.27h. The Tier 3 approach includes an adjustment tosubtract any uncalcined carbonate within sintering kiln dust (SKD) that is not returned to the kiln. If the SKD is
fully calcined, or all of it is returned to the kiln, this SKD correction factor becomes zero. Tier 3 is still considered
to be good practice in instances where inventory compilers do not have access to data on uncalcined SKD.
However, excluding uncalcined SKD may result in slightly overestimated emissions.
Limestones and shales (raw materials) may also contain a proportion of organic carbon (kerogen), and other raw
materials (e.g., fly ash) may contain carbon residues, which would yield additional CO2 when burned. Theseemissions typically are not accounted for in the Energy Sector, but if carbon-containing raw materials are used
extensively, inventory compilers should endeavour to see if they are included in the Energy Sector. Currently
however, there is insufficient data on the kerogen or carbon contents of non-fuel raw materials for mineralprocesses to allow a meaningful default value related to the average kerogen content of raw materials to beprovided in this chapter. For plant-level raw material-based calculations (Tier 3) where the kerogen content is high(i.e., contributes more than 5 percent of total heat), it is good practice to include the kerogen contribution toemissions.
The Tier 3 approach will likely only be practical for individual plants and countries that have access to detailed
plant-level data on the carbonate raw materials. Emissions data collected at the plant level should then be
aggregated for purposes of reporting national emissions estimates. It is recognized that frequent calculations ofemissions based on direct analysis of carbonates could be burdensome for some plants. As long as detailed
chemical analyses of the carbonate inputs are carried out with sufficient frequency to establish a good correlation
between the carbonates consumed at the plant level and the resulting alumina production, the sinter output may
then be used as a proxy for carbonates for emissions calculations in the intervening periods. That is, a plant may
derive a rigorously-constrained emission factor for the plant’s alumina, based on periodic calibration to thecarbonate inputs and outputs.

EQUATION 4.27H (NEW)
TIER 3: EMISSIONS BASED ON CARBONATE RAW MATERIAL INPUTS TO THE SINTERING KILN()

CO2 Emissions =∑ M oi • CiCO2 + ELC + EFs • M s + (0.71 CNa2O • Vs ) / 1000i

– Esp – Erm – ESKD + Enf – Ecc
Where:
CO2 Emissions= total emissions of CO2 from sintering kiln, tonnes

Σi (Moi • CiCO2 )= CO2 emissions from carbonates in bauxite or nepheline ore decomposed in kiln,
tonnesMoi= mass of i ore recalculated per dry conditions consumed in the kiln, tonnes

Cico2= the weighted average content of CO2 in i bauxite (nepheline) ore according tochemical analysis and assumption that 100 percent calcination will be achieved(in the absence of chemical analysis results, the content of CO2 in nephelines isdetermined as the difference in loss on ignition and SO3), as given by Equation
4.27k), fraction

ELC= СО2 emissions released from limestone calcination, tonnes СО2. The
calculation shall be done in accordance to Tier 3 approach described in Volume
3 IPPU, Chapter 2, Section 2.3. To avoid double counting before applying thismethod it is necessary to check if limestone usage data from alumina plant isalready considered at national level and CO2 emissions from lime calcination are2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories

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already considered in lime production data. If limestone usage for sintering
process at alumina plants has not been considered at national level, this process
shall be considered as source related to alumina production emission. If theemissions are considered as lime calcination emissions they shall be removed
from calculations by this formula.
EFs • Ms

= CO2 emissions from soda carbonate decomposition, tonnes. To avoid double
counting before applying this method it is necessary to check if this source isalready considered at national level. If soda decomposition in sintering process
at alumina plants has not been considered at national level, this process shall beconsidered as source related to alumina production emission. If the emissions
accounted for in Volume 3 (under Industrial Processes and Product Use),
Chapter 2 (Mineral Industry Emissions), Section 2.5 (Other Process Uses ofCarbonates) they shall be removed from calculations by this formula.

EFs= emission factor for soda carbonate forwarded to the kiln with ore, tonnes СО2/ tonnes soda carbonate (see Table 2.1 Chapter 2 Mineral Industry emissions)Ms= mass of soda forwarded to the kiln with ore, tonnes(0.71 CNa2O • Vs) / 1000

= CO2 emissions from the decomposition of soda contained in a soda solution,
tonnes0.71= stoichiometric conversion factor of CO2 from Na2O. Na2O is measure in thesoda solution

CNa2O= concentration of sodium oxide (carbonate) in the soda solution, forwarded to
the kiln, g/L

Vs= volume of soda solution, m3

Esp= СО2 emissions captured during Carbonisation process and contained in
produced sodium carbonate, tonnes СО2 (as given by Equation 4.27i)

Erm= Potential CO2 emissions based on the mass of carbon in bauxite or nepheline
residue, that is not emitted because some carbon absorbed by residue and stored
at bauxite or nepheline residue areas, tonnes (refer to Equation 4.27l)

ESKD= CO2 emissions from un-calcined SKD not recycled to the kiln, tonnes (refer toEquation 4.27j)

Enf= CO2 emissions from carbon-bearing non-fuel materials (as given by Equation
4.27m), tonnes

Ecc= CO2 absorption through use of circulating water collected frombauxite/nepheline storage residue area and/or absorption through bauxite residue
neutralization (as given by Equation 4.27n), tonnes

EQUATION 4.27I (NEW)EMISSIONS CAPTURED DURING CARBONISATION PROCESS AND CONTAINED IN PRODUCEDSODIUM CARBONATEE=
EFs • M soutsp
Where:
Esp= СО2 emissions captured during Carbonisation process and contained in produced sodium
carbonate, tonnes

EFs= emission factor for soda carbonate forwarded to the kiln with ore tonnes СО2 / tonnes soda
carbonate (see Table 2.1 Chapter 2 Mineral Industry emissions)

Msout = mass of soda produced for using out of plant, tonnes

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EQUATION 4.27J (NEW)EMISSIONS FROM UN-CALCINED SKD NOT RECYCLED TO THE KILN=
ESKD

( ( M + M ) • E /100% – M ) • C
dr

dnr

ac

dr

CO2

OR

ESKD = ( M d • Eac /100% – M dr ) • CCO2
Where:ESKD = CO2 emissions from un-calcined SKD not recycled to the kiln, tonnes
Mdr= mass of SKD recycled to the kiln, tonnes

Mdnr= mass of SKD not recycled to the kiln (= ‘lost’ SKD), tonnes

Md= mass of SKD forwarding to exhausted gases cleaning facilities at sintering kilns, tonnes

Eac= efficiency of exhausted gases cleaning facilities at sintering kilns, percentage

CCO2 = carbon content in dust recalculated in CO2, fraction

EQUATION 4.27K (NEW)WEIGHTED AVERAGE CONTENT CO2 IN ‘I’ BAUXITE (NEPHELINE) ORE

CiCO2 = ∑ j ( EFj • M j )Where:CiCO2= the weighted average content of CO2 in i bauxite (nepheline) ore according to chemical analysis,
assuming 100 percent calcination of the carbonate, fraction

EFj= emission factor for the particular carbonate j, tonnes CO2 / tonnes carbonate (see Table 2.1 Chapter
2 Mineral Industry emissions)Mj= mass fraction of carbonate j consumed in the kiln, fraction

EQUATION 4.27L (NEW)POTENTIAL EMISSIONS FROM BAUXITES (NEPHELINES) RESIDUE

Erm= 44 /12 • M br • Cc
Where:Erm= Potential CO2 emissions based on the mass of carbon in bauxite or nepheline residue, that is not
emitted because some carbon absorbed by residue and stored at bauxite or nepheline residue areas,
tonnesMbr= mass of dry bauxite or nepheline residue disposed, tonnes

Cc= mass fraction of C in dry bauxite or nepheline residue, fraction

EQUATION 4.27M (NEW)EMISSIONS FROM CARBON-BEARING NON-FUEL MATERIALS

Enf = ∑ k ( M k • X k • EFk )Where 18:

18 The ignored CO emissions from non-carbonate carbon (e.g., carbon in kerogen, carbon in fly ash) in the non-fuel raw
2materials can be considered negligible if the heat contribution from kerogen or other carbon is < 5% of total heat (from fuels).

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Enf= CO2 emissions from carbon-bearing nonfuel materials, tonnesMk= mass of organic or other carbon-bearing non-fuel raw material k, tonnes

Xk= fraction of total organic or other carbon in specific non-fuel raw material k, fraction

EFk= emission factor for kerogen or other carbon-bearing nonfuel raw material k, tonnes CO2/tonne
carbon-bearing nonfuel raw material

EQUATION 4.27N (NEW)CO2 ABSORPTION THROUGH USE OF CIRCULATING WATER COLLECTED FROMBAUXITE/NEPHELINE STORAGE RESIDUE AREA AND/OR ABSORPTION THROUGH BAUXITERESIDUE NEUTRALIZATION

Ecc = Vgas • CCO2 • DCO2 • GTECO2 /100
Where:Ecc= CO2 absorption through use of circulating water collected from bauxite/nepheline storage
residue area and/or absorption through bauxite residue neutralization, tonnes

Vgas= exhaust gas volume forwarded to exhaust gas treatment facility, cubic meters

Cco2= CO2 concentration in exhaust gas (instrumental measures), fraction of volume

Dco2= CO2 destiny under normal conditions, tonne/cubic meters

GTEco2= exhaust gas treatment facility efficiency (instrumental measures), percentage

4.4.5.3

C HOICE OF EMISSION FACTORS FOR ALUMINA

PRODUCTION

Emissions factors for Sintering can be chosen based on available data. In the case that site-specific data is notavailable, Tier 1 default emission factors can be used. Emissions factors for lime production are provided inVolume 3, Section 3.3.1.2.

TIER 1 METHOD FOR SINTERINGThe implementation of sintering processes is determined by bauxite quality (alumina content), carbonates andsilica content in the ore which can vary significantly. Based on existing process data from operating plants, Tier 1
emissions factors were derived for Bayer-sintering processes and the nepheline-sintering process (NP), to be
applied in Equation 4.27g (see Table 4.17a). For Bayer-sintering process Tier 1 emissions factors can be applied
for both parallel (BSP) and sequential (BSS) processes.
TABLE 4.17A (NEW)TECHNOLOGY SPECIFIC DEFAULT EMISSION FACTORS FOR THE CALCULATION OF CO2 EMISSIONS FROM ALTERNATIVESINTERING PROCESSES (TIER 1 METHOD)
Technology

EFSintAl2O3 (tonne CO2/tonne Al)a

Uncertainty Range (%)b

Bayer-sintering (BSP and BSS)

0.81

-8/+4

Nepheline-sintering process (NP)

2.46

-2/+4

The defaults based on the following process data – alumina content (Al2O2) is 45.8% in bauxites and 26.2% in nepheline ore. Bauxite
and nepheline consumption in sintering is very depend on Al2O2 content and in case of poor ore where Al2O2 content is out of range EF
shall be higher and uncertainty level will increase.

ab
Uncertainty range is based on calculations from alumina plants that operate sintering kilns for several years based on alumina content as
described above.

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TIER 2 METHOD FOR SINTERINGCountry-specific emission factors should be collected based on knowledge of technologies (technological routes)
implemented at a country’s facilities and also based on data for lime (country-specific carbon content). Tier 1
method then should be applied.
If alumina plants have sintering processes, site specific data should be obtained relating to the volume of alumina
production, percent of alumina produced with sintering. Plant specific volume of alumina production, percentage
of alumina produced with sintering and information about the bauxite sources or technology and country specificemissions factors shall be calculated and should be provided for each national-level GHG emissions calculation
campaign.

TIER 3 METHOD FOR SINTERINGThe Tier 3 emission factors are based on the actual CO2 content of the carbonates present (see Equation 4.27h inthis chapter and Table 2.1 of Volume 3, Chapter 2 Mineral Industry Emissions).). The Tier 3 approach requires
the full accounting of carbonates (species and sources).
CO2 emissions captured by other CO2 capturing technologies can be calculated using site specific data only. Where
such data is unavailable, CO2 emissions captured do not considered in CO2 emissions calculation.
If there is no site-specific data for mass of carbon in bauxite or nepheline residue, the following data can be used
as worldwide figures:•

CO2 in bauxite and nepheline residue 1 percent of dry content with a ± 50 percent uncertainty range 19.

Em iss io ns co rr e ct ion fa ctor fo r s in te r ing k iln du st (SKD)
Dust may be generated at various points in the kiln line apparatus used for sintering. The composition of this dust
can vary depending on where it is generated but all may be included under the term ‘sintering kiln dust’ (SKD).
SKD includes particulates derived from the raw materials, and the original carbonate component of the dust may
be incompletely calcined. SKD can be efficiently captured by dust control technology and then recycled to the kiln
(the preferred practice), or it may be directly returned to the kiln in the combustion air, or it may be disposed ofafter capture. The degree to which SKD can be recycled to the kiln depends on various considerations and usually
100 percent of collected dust are returned to the kiln. Any SKD not recycled to the kiln is considered to be ‘lost’
to the process and emissions associated with it will not be accounted for in the sintering process. To the degree
that the lost SKD represents calcined carbonate raw materials, the emissions from these calcined raw materials
represent a subtraction in the Tier 3 calculation. The kiln dust may consist of dust from raw materials as well as
dust from the burning of liquid or solid fuels. In that case where combustion and process emissions are to bereported separately, e.g. for alumina production, it is good practice for inventory compilers ensure that the carbon
in the dust related to fuel combustion is not double counted. In these cases, the total amount of C in the dust fromfuel burning should preferably be extracted from IPPU source categories in proportion to the amounts of CO2
generated in these source categories.

4.4.5.4

C HOICE OF ACTIVITY DATATIER 1 METHOD
In Tier 1, national-level data should be collected only for those plants where lime calcination processes are part ofalumina production process. However, calcined lime purchased from other producers should not be considered to
avoid double counting.
If a proportion of calcined lime is produced for uses other than alumina production, to avoid double counting CO2
emissions from carbonates decomposition at the lime calcination kiln shall be related to alumina production in the
proportion of lime used for alumina production only. CO2 emissions related to other uses of calcined lime shall bereported as emissions related to lime calcination described at Chapter 2 Section 2.3. The detailed information
about choice of activity data for lime production please refer to Section 2.3.1.3 in Volume 3, Chapter 2.
If alumina plants have sintering processes, site specific data should be obtained relating to the volume of alumina
production, percent of alumina produced with sintering. Plant specific volume of alumina production, percentage

19

The uncertainty range is based on expert judgment.

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Volume 3: Industrial Processes and Product Useof alumina produced with sintering and information about the bauxite sources or technology should be provided
for each national-level GHG emissions calculation campaign.

TIER 2 METHOD
In Tier 2, national-level data should be collected only for those plants where sintering/lime calcination processes
are part of alumina production process. However, calcined lime purchased from other producers should not be
considered to avoid double counting.

TIER 3 METHODSFor lime production process refer to Section 2.3.1.3 Choice of Activity Data in Volume 3, Chapter 2.
The type of activity data required for Tier 3 is likely available only at individual plants. Any reporting entity using
Tier 3 should ensure that all carbonate inputs (i.e., types, amounts, all sources) to the kiln are fully investigated aspart of the initial implementation of the Tier 3 method, and the full investigation repeated whenever there is any
significant change in materials or processes. After a full analysis of the carbonate inputs is completed, andassuming that no significant change in the composition of materials or production process takes place, it isconsistent with good practice to develop a rigorous plant-specific emission factor based on the carbonate input
analysis and apply that emission factor to sintering process. Subsequently, the sintering production data may thenbe used for the carbonate calculations to estimate emissions. To be consistent with good practice, this linkage
should be periodically recalibrated.
In general, data related to carbonated input materials should be collected annually. However, it is likely that there
could be a carbonate component within the mass of carbon in bauxite or nepheline residue, emissions from uncalcined SKD not recycled to the kiln, and perhaps some other fuels (emissions from carbon-bearing nonfuelmaterials). If, during the full investigation, it is determined that the amount of carbonates from non-major sources
is small (e.g., less than 5 percent of total carbonate) the plant can apply a constant value for the minor source(s) inintervening years before the next full investigation. Recognizing that estimating activity data for these smaller
sources may lead to analytical (and other) errors, it may be assumed for emission calculation purposes that theminor source of carbonate is CaCO3, but this assumption should be transparently documented.
Activity data should exclude any carbonates that are not fed into the kiln.

4.4.5.5

C OMPLETENESS

Alumina production data may be available in national statistical databases, or could be collected, if such data havenot been published in national statistics.
Completeness is a particularly important issue to consider where plant specific data are used to estimate nationalemissions using Tier 3. Under Tier 3, it is important that all alumina plants with lime production and sintering
processes are considered, and that all carbonates consumed in the sintering process are included in the emission
calculation. Plants with bauxites/nephelines sintering processes are well identified in each country, but data on thefraction weight of carbonates consumed may not be readily available. In order for the Tier 3 method to beconsidered ‘complete’, all carbonates consumed must be recorded.
In countries where only a subset of plants with lime production and bauxites/nephelines sintering processes report
data for the Tier 3 method, it may not be possible to report emissions using a Tier 3 for all facilities during thetransition. Where data on the carbonate inputs are not available for all plants to report using Tier 3, it may bepossible to determine the share of production represented by non-reporting plants and use this information toestimate the remaining emissions using Tier 1 in order to ensure completeness during the transition period.
The potential for double counting also should be considered. For example, it is good practice for inventory
compilers to review statistics used to estimate emissions from the source category ‘Other Process Uses ofCarbonates’ and ‘Lime production’ to ensure that emissions reported in that source category do not result from theuse of these carbonates in alumina production. Where carbonates are used for alumina production, it is goodpractice to report the emissions under Alumina Production. Finally, inventory compilers should include only
process-related emissions from alumina production in this source category. To avoid double-counting, it is goodpractice to account for combustion-related emissions in the Energy volume.
There is one additional issue that, while not included in the current methodology, may become relevant forconsideration in the future. Sodium alkaline contained in bauxite/nepheline residue area can re-absorb atmosphericCO2. However, the rate of carbonation is very slow (years to centuries).

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4.4.5.6

D EVELOPING A CONSISTENT TIME SERIESIt is good practice to collect site specific data where possible for all inventory years. However, often it can bedifficult to collate historic data for closures, closed operations or if significant changes in changes in technology
or sourcing of bauxites/nephelines has taken place. In such cases, inventory compilers can consult industry experts
to assist with extrapolation of CO2 emission figures (e.g. normalization by volume of alumina production or basedon applying of data from similar plants in the reporting country or average worldwide figures for similar
technology). See also Chapters 2 and 5 of Volume 1 of 2006 IPCC Guidelines.
For lime production, refer to Section 2.3.1.5 in Chapter 2.

4.4.6

Uncertainty assessment for alumina production

Uncertainty estimates for bauxite/nepheline sintering processes result predominantly from uncertainties associatedwith activity data, and to a lesser extent, from uncertainty related to the emission factor.
Uncertainty estimates for lime production is described at Section 2.3.2 Uncertainty assessment in Chapter 2
Volume 3 of 2006 IPCC Guidelines.

4.4.6.1

E MISSION FACTOR UNCERTAINTIESFor Tier 1, the major uncertainty component is associated with the emission factor for sintering.
For Tier 2 and 3, there is relatively little uncertainty associated with the emission factors of the source carbonates
because they are based on plant specific data, stoichiometric ratios and mass balance approaches.

4.4.6.2

A CTIVITY DATA UNCERTAINTIESThe uncertainty for percentage of bauxite/nepheline processing at sintering process is moderate. The level of
uncertainty is indicated in the Table. 4.17b. The uncertainty in data on alumina production tonnages is about 1
percent.
For Tier 3, the uncertainty in data on weight or mass of i ore recalculated per dry conditions consumed in the kiln
tonnages, is about 1-2 percent. Collecting data from individual producers (if complete) rather than using national
totals will reduce the uncertainty of the estimate because these data will account for variations in conditions at theplant level. Except for SKD the greatest sources of uncertainty associated with Tier 3 are the uncertainties
associated with identification of carbonate species (1-5 percent) and the weight of raw materials.
Although emissions are much smaller than from carbonates, there may be considerable uncertainty associated withestimating emissions from SKD in Tier 3 if plants do not weigh the SKD that is not recycled to the kiln or if theplants lack SKD scrubbers. Where the weight and composition of SKD are unknown for a plant, the uncertainty
will be higher. As an example, an estimate of the uncertainties for different factors is presented in equations 4.27h4.27n. The uncertainties are presented in Table 4.17b and are approximate component uncertainties – that is, they
are those associated with a particular operation or activity in the bauxite/nepheline processing at sintering process.
In order to quantify uncertainty for bauxite/nepheline processing at sintering process, the default uncertainties
provided in Table 4.17b should be combined.

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TABLE 4.17B (NEW)DEFAULT UNCERTAINTY VALUES FOR BAUXITE/NEPHELINE SINTERING PROCESSES
Uncertaintya

Comment

Tier

Chemical Analysis / Composition
1-3%

Percentage of bauxite processing at sintering process

1

10%

Estimation of percentage of bauxite processing at sintering process

1-2/+4%

Emission factor for sintering (NP)1

-8/+4%

Emission factor for sintering (BSP and BSS)

1

10%

Assumption that emission factor for sintering is permanent over the years

1

5%

The content of sodium oxide (carbonate) in the soda solution, forwarded to the kiln

3

15%

Estimation of content of sodium oxide (carbonate) in the soda solution, forwarded to the kiln

3

5%

The weighted average content of C in dry bauxite/nepheline residue

350%

Estimation of weighted average content of C in dry bauxite/nepheline residue

3

1%

Weight or mass share of particular carbonate consumed in the kiln

32%

Fraction calcination achieved for carbonates

3

Assumption 100% of fraction calcination achieved for carbonate

3

3%

Weight or mass of organic or other carbon-bearing nonfuel raw material

3

3%Fraction of total organic or other carbon in specific nonfuel raw material

350%

Estimation of weight or mass of organic or other carbon-bearing nonfuel raw material

350%

Estimation of fraction of total organic or other carbon in specific nonfuel raw material

3

1-3%

Kerogen (or other non-carbonate carbon) determination

3

10%

CO2 concentration in exhaust gas

3

5%

Exhaust gas treatment facility efficiency

31%

CO2 destiny under normal conditions

3

10-20%

Production Data

4.78

1-2%

Reported (plant-level) alumina production data

1, 3

10%

Use of estimated country (or aggregated plant) production data (national statistics).

1

1-2%

Weight or mass of ore recalculated per dry conditions consumed in the kiln

3

10%

Estimation of weight or mass of ore recalculated per dry conditions consumed in the kiln

3

1-2%

Weight or mass of soda forwarded to the kiln with ore

310%

Estimation of weight or mass of soda forwarded to the kiln with ore

32%Volume of soda solution

3

35%

Estimation of volume of soda solution

3

1-2%

Weight or mass of soda produced for using out of plant35%

СО2 emissions captured by other СО2 capturing technologies

3

15%

Estimation of СО2 emissions captured by other СО2 capturing technologies

35%

Mass of bauxite/nepheline residue disposed

3

10%

Estimation of bauxite/nepheline residue disposed

3

2%

Exhaust gas volume forwarded to exhaust gas treatment facility

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TABLE 4.17B (NEW) (CONTINUED)DEFAULT UNCERTAINTY VALUES FOR BAUXITE/NEPHELINE SINTERING PROCESS
Uncertaintya

Comment

Tier

SKD

a

1-2%

Weight or mass of SKD recycled to the kiln

3

10%

Estimation of weight or mass of SKD recycled to the kiln

3

1-2%

Weight or mass of SKD not recycled to the kiln

3

10%

Estimation of weight or mass of SKD not recycled to the kiln

3

1-2%

Efficiency of exhausted gases cleaning facilities at sintering kilns

3

10%

Estimation of efficiency of exhausted gases cleaning facilities at sintering kilns

3

1-2%

Carbon content in dust recalculated in CO2

3

10%

Estimation of carbon content in dust recalculated in CO2

3

Uncertainty estimates are based on expert judgement.

4.4.7

4.4.7.1

Quality Assurance/Quality Control (QA/QC),
Reporting and Documentation for alumina
production
Q UALITY A SSURANCE / Q UALITY C ONTROL (QA/QC)

In addition to the general guidance on QA/QC, specific procedures of relevance to this source category are outlined
below.

COMPARISON OF EMISSIONS ESTIMATES USING DIFFERENTAPPROACHES
Comparisons could be made between estimated emissions using different tiers. For example, if a bottom-up
approach is used to collect activity data (i.e., collection of plant-specific data), then inventory compilers should
compare the emissions estimates to the estimates calculated using national production data alumina production(top-down approach). In cases where a hybrid Tier 1 or Tier 3 approach is used during a transition period, it isconsidered good practice also to estimate emissions for all facilities using the lower Tier in order to compare theresults of the analysis to the results derived using the hybrid approach. The results of such comparisons should berecorded for internal documentation, including explanations for any discrepancies.

REVIEW OF EMISSION FACTORS
Inventory compilers should compare aggregated national emission factors with the IPCC default factors in orderto determine if the national factor is reasonable relative to the IPCC default. Differences between national factors
and default factors should be explained and documented, particularly if they are representative of different
circumstances.
If the aggregated top-down approach is used, but some limited plant-specific data are available, inventory
compilers should compare the site or plant level factors with the aggregated factor used for the national estimate.
This will provide an indication of the reasonableness and the representability of the data.

SITE-SPECIFIC ACTIVITY DATA CHECKFor site-specific data, inventory compilers should review inconsistencies between sites to establish whether theyreflect errors, different measurement techniques, or result from real differences in emissions, operational

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conditions or technology. For alumina production, inventory compilers should compare plant data with other plants
in the country.
Inventory compilers should ensure that emission factors and activity data are developed in accordance withinternationally recognised and proven measurement methods. If the measurement practices fail this criterion, thenthe use of these emissions or activity data should be carefully evaluated, uncertainty estimates reconsidered, andqualifications documented. If there is a high standard of measurement and QA/QC in place at most sites, then theuncertainty of the emissions estimates may be revised downwards.

4.4.7.2

R EPORTING AND D OCUMENTATION

It is good practice to document and archive all information required to produce the national emissions inventory
estimates. Specific documentation and reporting relevant to this source category follow.

TIER 1 METHOD
Any information regarding the carbonates content of sintering feed should be documented, including use of default
values different from those discussed in section 4.4.5.3.

TIER 2 METHOD
Any county-specific information should be documented (technologies, amount of alumina produced by eachtechnology type, amount and quality of lime used, etc.)

TIER 3 METHOD
When documenting the Tier 3 method it is important to document all the procedures undertaken and methodologies
used to identify the weight fraction and identities of all carbonates, including carbonates incorporated in any raw
materials along with the corresponding emission factors.
Estimating total emissions from carbonate inputs can overestimate emissions if the carbonates are not fully
calcined. Any corrections should be documented. This includes documenting the fraction calcination of the raw
materials and the quantity and fraction calcination of the SKD.
It is likely that plants will find it impractical to undertake chemical analyses of all raw material inputs on a daily
basis for the purpose of CO2 calculations. Instead, it is good practice for a full analysis to take place at each facility
on a number of occasions throughout the year to fully characterise the carbonate inputs. Facilities will likely
develop a relationship between carbonate input and alumina production that will be applied to the plant’s routine
calculation alumina production with sintering for intervening periods. In addition to identifying all procedures
used to calculate emissions from the carbonate inputs, all steps necessary to identify the relationship between
carbonate input and alumina production should be documented.
All underlying information should be documented and reported, it is not considered good practice to report just
final emissions estimates.

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4.5

MAGNESIUM PRODUCTION

No refinement.

4.6

LEAD PRODUCTION

No refinement.

4.7

ZINC PRODUCTION

No refinement.

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4.8

RARE EARTHS PRODUCTION

This sub-chapter 4.8 “Rare Earths Production” provides new guidance for greenhouse gas (GHG) emissions fromthe primary production of rare earth (RE) metals and alloys 20 , specifically CO2 and perfluorocarbon (PFC)
emissions. Since the 2006 IPCC Guidelines do not have existing guidance on emissions from the rare earths
industry, this is an entirely new sub-chapter, and follows on sub-chapter 4.7 Chapter 4 Volume 3 of the 2006 IPCC
Guidelines.

4.8.1

Introduction‘Rare earths’ is used to refer to the group of 17 chemically similar metallic elements of scandium (Sc), yttrium (Y)and the lanthanides, i.e.: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm),samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er),thulium (Tm), ytterbium (Yb) and lutetium (Lu). The raw materials and trading goods are often in the form of rareearth oxides (REO).
Worldwide, primary production of many RE metals and alloys is carried out using a molten fluoride-salt
electrolytic reduction process that is similar to primary aluminium’s Hall-Heroult process 21 (refer to sub-chapter
4.4). According to (Vogel & Friedrich 2015; Vogel & Friedrich 2018; Zhang et al. 2018), this involves:•

Dissolving and electrolytically reducing REOs (e.g. Nd2O3) in a molten salt of rare earth fluorides (REF3) andlithium fluoride (LiF) – an example composition is 85 percent wt NdF3, 10 percent LiF and 5 percent Nd2O3
for Nd metal production;•

Carbon anodes (e.g. graphite), which are consumed in the process;•Cathodes, which are either inert (e.g. tungsten cathodes for Nd metal production) or are consumed in theprocess (e.g. Fe cathodes for Dy-Fe alloy production);•

A process that is carried out at high temperature (~1050-1100°C);•

Depending on the technology, a process that may be periodically interrupted or disturbed by anodereplacements, cathode removal/replacement and removal of liquid RE metal/alloy, etc.

Nd is one of the most commonly produced RE metals by this process. Other RE metals and alloys produced via
this route include: Pr, Pr-Nd, La, Dy-Fe, Gd-Fe, Ho-Fe, Ce, La-Ce, Y-Mg and mischmetal (Vogel & Friedrich2018).
Alternative routes for RE metal and alloy production are outside the scope of these guidelines, since they are either
not employed on an industrial scale or do not generate GHGs (Vogel & Friedrich 2018). These include chloridesalt electrolytic reduction (now largely replaced by the fluoride-based process) and calciothermic reduction (e.g.
for production of samarium for Sm-Co magnets).
Industrial fluoride-based rare earth smelters vary in terms of electrical current (and hence size), the number andconfiguration of anodes and cathodes, and the level of automation in the process. Currently, the most widely usedtechnologies are those at lower amperage (~5-6 kA) – these typically employ small round-shaped cells, with only
single (or several) vertical anodes and cathodes and typically have very low levels of automation. Higher amperagetechnologies typically are larger, oval or rectangular shaped cells and are equipped with multiple vertical anodes
and/or cathodes (Wen et al. 2004; Wen et al. 2012; Vogel & Friedrich 2015).
In general, the level of automation in rare earth production is considerably lower than that found in primaryaluminium production (sub-section 4.4). However, some newer production technologies may be equipped with
automatic process control features, including automatic feeding of REOs and automatic detection of anode effects,
in order to increase production efficiency and reduce perfluorocarbon GHG emissions (refer to section 4.8.2.3).

20

CO2 emissions associated with the production of electricity from fossil fuel combustion to produce rare earth metals andalloys are covered in Volume 2: Energy.

21

Due to similarities between the primary aluminium and rare earth metal smelting processes (both produce metal fromelectrolysis of metal oxides in molten fluoride-salts, using consumable carbon anodes), the guidelines here for the rare earths
industry have been adapted using existing guidelines for primary aluminium production (2006 IPCC Guidelines, Volume 3,
Chapter 4, sub-chapter 4.4) as a basis. Although both processes generate CO2 and PFC emissions through similar fundamental
mechanisms, there are clear differences in technology and cell design, production scale, cathode and raw materials, operating
conditions (amperage, voltage, temperature) and particularly levels of automation. Therefore, the guidance provided here is
specific to current understanding of rare earth metals production.

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In the fluoride-based rare earths smelting process, the most significant GHG process emissions are (Liu et al. 2001;
Vogel et al. 2017; Cai et al. 2018):
1.

CO2 emissions from the consumption of carbon anodes in the electrolytic reaction converting rare earthoxides to rare earth metals;

2.

PFCs emissions of CF4 and C2F6 during anode effects. While not commonly observed, very low levels of
C3F8 and trace levels of other PFCs (e.g. c-C4F8 and C4F10) have also been reported (Cai et al. 2018).

CO is another major process emission; SO2 might also be emitted in very small amounts.
The decision trees in Figure 4.17 and Figure 4.18 provide guidance for selecting a methodology to estimate CO2
and PFC emissions, respectively, from rare earth metal production. Since default emission factors have been
provided, all inventory compilers in countries with rare earth metal production should be able to implement at aminimum level the Tier 1 method and thereby ensure completeness of reporting.

4.8.2
4.8.2.1

Methodological Issues
C HOICE OF METHOD FOR CO 2 EMISSIONS FROM PRIMARY

RARE EARTH METAL PRODUCTION

During normal operations, rare earth metals are produced at the cathode and carbon is consumed at the anode,
forming CO and CO2 gases by electrolysis, as per the generic electrolytic reduction reactions below for productionof any RE from REO (Liu et al. 2001; Vogel et al. 2017) :REx Oy + yC → xRE + yCO
REx Oy +yy
C → xRE + CO2
2
2

An example reaction for Nd metal production from its oxide is as follows:

Nd 2O3 + 3C → 2 Nd + 3CO
Nd 2O3 + 3 / 2 C → 2 Nd + 3 / 2 CO2
For rare earth alloys that are formed by alloying with a consumable iron cathode during production, an example isthe production of Dy-Fe alloy from its rare earth oxide; the reaction is as follows (Martinez et al. 2018):

Dy2O3 + 2 x Fe → 2 Dy − Fex + 3 CO
Dy2O3 + 2 x Fe → 2 Dy − Fex + 3 / 2 CO2While CO is the most dominant gas produced in these reactions (Liu et al. 2001; Vogel et al. 2017), it is assumed
that all CO gas oxidises in the process and is ultimately emitted to the atmosphere as CO2 gas (Vogel & Friedrich2018), as follows:

2CO + O2 → 2CO2
Most CO2 emissions therefore result from the electrolysis reaction of the carbon anode with rare earth oxides(REO). The consumption of carbon anodes is the principal source of process related CO2 emissions from primaryrare earth production. The reactions leading to CO2 emissions are relatively well understood and the emissions are
directly connected to the tonnes of RE metal or alloy produced, through the fundamental electrochemical equations
for RE oxide reduction at a carbon anode and oxidation from thermal processes. Both of these fundamental

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processes producing carbon dioxide should be included in process parameters routinely monitored at production
facilities, i.e. the net anode carbon consumed.
Due to a lack of published information, no other sources of process-related CO2 emissions have been consideredin these guidelines. For example, it is assumed that industrial rare earth facilities currently do not manufacture or‘pre-bake’ their own carbon anodes, but rather they purchase graphite anodes. This is the case in the Chinese rareearth metal industry in 2018 (expert opinion), given the much lower process volumes and smaller anode sizes
compared to the primary aluminium industry (which uses prebaked carbon anodes, refer to sub-chapter 4.4.2.1).
Hence GHGs from anode baking (and associated energy use) are not considered here.
The decision tree shown in Figure 4.17 describes good practice in choosing the CO2 inventory methodology
appropriate for national circumstances.

Figure 4.17 (New)

Decision tree for calculation of CO 2 emissions from primary rare earth(RE) metal production
Start

Is data available foranode consumption?

Yes

Is facility specific data on
anode composition available?

Yes

Calculate CO2 emissions
using Tier 3
Box 2: Tier 3No

No

Is this a key
category1?

No

Is RE metal
production data
available 2?

Yes

No

Collect anode data forTier 3 calculations

Estimate annual RE metal
production

Yes

Calculate CO2 emissions
using Tier 1
Box 1: Tier 1

Notes:
1. For discussion of key categories and use of decision trees, see Volume 1, Chapter 4, Methodological Choice and Identification of Key
Categories (noting Section 4.1.2 on limited resources).
2. For Tier 1 CO2 emissions calculation, the production data does not require differentiation of specific rare earth metals and alloys produced(Nd, Pr, Ce, La metals and/or Nd-Pr, Dy-Fe alloys, etc). There is also no need for further differentiation as to the type of rare earth cell
technology used at each facility.
3. The decision tree only provides a two-tiered methodology: Tier 1 using default emission factors, and Tier 3 using facility-specific anodeconsumption + anode composition data. An additional Tier 2 method using default factors for anode composition data (corresponding to Tier
2 in the CO2 decision tree for aluminium production, sub-chapter 4.4.2.1) has not been provided, since there is no default anode composition
data for rare earths publicly available.

Tie r 1 m ethod for CO 2 e m iss ion s – defa u lt emis s ion fac tor s
The Tier 1 method for calculating CO2 emissions is through multiplying a default emission factor by rare earth
metal production. Given the uncertainty associated with the Tier 1 method, it is good practice to use higher tier

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methods if CO2 from primary rare earths is a key category. Total CO2 emissions from all rare earth (RE) metals
and alloys produced are calculated according to Equation 4.35.
EQUATION 4.35 (NEW)PROCESS CO2 EMISSIONS FROM ANODE CONSUMPTION (TIER 1)

ECO2 = ∑ i  EFCO2 • ( AWbase / AWi ) • MPi 

Where:
ECO2= Total CO2 emissions from carbon anode consumption, tonnes CO2

EFCO2= CO2 default emission factor for RE metal/alloys, tonnes CO2/tonne RE metal

AWbase = Atomic weight of base case rare earth metal, i.e. neodymium = 144.24 g/mol
AWi= Atomic weight of rare earth metal/alloy type i, g/mol

MPi= Total metal production for RE metal/alloy type i, tonnes RE metal

Only one default CO2 emission factor has been provided in these guidelines, taking Nd metal as the base case –refer to Table 4.26. The scarcity of published data means that default emission factors are not available for other
RE metals and alloys. However, Equation 4.35 includes a factor to correct the default to account for differences inatomic weight among the RE metals. This factor is the atomic weight for Nd divided by the atomic weight of themetal or alloy actually produced. Taking Dy-Fe alloy as an example (assuming 80 percent Dy, 20 percent Fe byweight) 22, the atomic weight is 117.59 g/mol and the atomic weight ratio (AWbase / AWi) is 1.23. Note that Equation
4.35 could be used for more precise estimates of total CO2 emissions from RE metals production if more Tier 1
default factors for specific RE metals/alloys become available in the future. In that case, where an emission factor
for a particular RE metal was applied to that RE metal, the atomic weight ratio (AWbase / AWi) would simply be set
to 1.

Tier 3 method for CO 2 emissions – by facility-specific carbon mass balance
In the Tier 3 method, CO2 emissions are calculated using a mass balance approach that assumes that the carbon
content of net anode consumption 23 is all ultimately emitted to the atmosphere as CO2 gas 24. The Tier 3 method
uses actual concentrations of anode impurities from each facility. The choice of method between the Tier 1 andTier 3 method will depend on whether process data for (i) net carbon anode consumption and (ii) baked anodecomposition are both available from individual facilities. Unfortunately, a more generic Tier 2 method (similar tothat for aluminium production, in sub-section 4.4.2.1) using default factors for net anode consumption and anodecomposition (including impurity levels) is not available due to the scarcity of published information.
CO2 emissions for the Tier 3 method are calculated according to Equation 4.36. This requires facility-specificoperating data for all the components in Equation 4.36. Note this assumes the same anode composition is used for
production of all RE metals and alloys; where the anode composition differs, replace Impa with Impi, the impurity
content of the anodes used to produce each type of RE metal / alloy.
EQUATION 4.36 (NEW)PROCESS CO2 EMISSIONS FROM ANODE CONSUMPTION (TIER 3)

ECO2 =   [(100∑i ( NACi • MPi ) •− Impa ) /100] • (44 /12)
Where:
22 Taking 100g basis for a Dy-Fe alloy with 80:20 wt fraction of Dy to Fe, the molar composition is 0.492 mol Dy, 0.358 mol

Fe, or 58% mol Dy, 42% mol Fe. The atomic weight is therefore = 100 g / (0.492 + 0.358) mol = 117.59 g/mol.

23‘Net anode consumption’ (NAC) refers to the total anode consumption per tonne of metal, minus any unused or ‘spent’
anode material when old anodes are exchanged for new anodes. This unused or ‘spent’ anode material is not consumed in
the electrolysis process but might be recycled to make new anodes.

24 While CO is the most dominant gas product from the rare earths electrolytic reduction reaction (Liu et al. 2001), it is assumed

that any CO formed eventually is converted to CO2 gas. The same carbon mass-balance approach is assumed for the primaryaluminium industry, in sub-chapter 4.4.2.1.

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ECO2= Total CO2 emissions from carbon anode consumption, tonnes CO2

NACi= Net anode consumption per tonne of RE metal/alloy type i, tonnes anode/tonne RE metal

MPi= Total metal production for RE metal/alloy type i, tonnes RE metal

Impa= Total content of non-carbon impurities (e.g. sulphur, ash, etc) in baked carbon anodes, wt %44/12

= CO2 molecular mass: carbon atomic mass ratio, dimensionless

Equation 4.36 can be applied to each rare earth smelter in the country and the results summed to arrive at total
national emissions.
It is possible to use a hybrid Tier 1 and 3 approach if facility specific net anode consumption and composition data
(impurity content, e.g. ash, sulphur, etc) are not available for each smelter.

4.8.2.2

C HOICE OF EMISSION FACTORS FOR CO 2 EMISSIONS FROMPRIMARY RARE EARTH METAL PRODUCTION
Tier 1 method for CO 2 emissions

Table 4.26 lists the default emission factors for CO2 per tonne of RE metal, for use in Equation 4.35. Given the
scarcity of published data and since only minor differences in emission factors are expected across different RE
metals and alloy types 25, only one default emission factor is provided for all RE metals. This uses Nd metal
production as the basis, since it is the most common RE metal produced via fluoride-salt electrolysis. It is goodpractice to check the EFDB as a source for future CO2 emission factors for rare earth metals production.
TABLE 4.26 (NEW)
TIER 1 DEFAULT EMISSION FACTORS FOR CALCULATING CO2 EMISSIONS FROM ANODE CONSUMPTION
Rare Earth Metal / Alloyi
Nd metal, and all other Rare Earthmetals/alloys

Emission Factor, 𝑬𝑬𝑬𝑬𝑪𝑪𝑪𝑪𝑪𝑪(tonnes CO2/tonne RE metal)

Uncertainty Range(%)

0.56 a,b-22/+24% c

Source:CO2 default emission factor is based on a net anode carbon consumption of 152 kg C/tonne RE metal (average anode consumption
reported from 4 industrial production lines in China - (Cai et al. 2018)) and converting this to CO2 by mass balance, assuming 100%
conversion of anode carbon to CO2, an approach consistent with that used in aluminium production (refer to section 4.4.2.1). These
production lines are considered representative of current technology in China, where >90% of global RE metal was produced in 2018
(Cai et al. 2018); as such the default emission factor is considered representative of current global RE metal production, via fluoride-salt
electrolysis. The emission factor is also consistent with values from a first principles / mass balance approach (see note b).

a

A first principles calculation for CO2 was done by taking electrolysis of Nd2O3 to Nd metal as a basis (see Section 4.8.2.1 forstoichiometric reactions), assuming a gas production ratio of ~75% CO, 25% CO2 by direct electrolysis at 1050°C and anode current
density of 1.0 A/cm2 (Liu et al. 2001); Vogel and Friedrich (2015). CO2 is then calculated assuming: (i) all CO is ultimately oxidised toCO2, (ii) process has a 75% faradaic current efficiency (% anode carbon electrolytically consumed to produce metal), and (iii) an
additional 10% anode carbon consumed via non-electrolytic processes (oxidation of carbon due to exposure with air). The obtained net
anode carbon consumption (150 kg C / tonne RE metal) is consistent with that used for the default CO2 emission factor.
b

TABLE 4.26 (NEW) (CONTINUED)TIER 1 DEFAULT EMISSION FACTORS FOR CALCULATING CO2 EMISSIONS FROM ANODE CONSUMPTION
Assuming the default CO2 emissions factor represents a current efficiency of 75%, an uncertainty range of -22%/+24% from the default
CO2 factor might be expected if individual facilities operate at a different current efficiency level (e.g. 60 to 95%), based on first principle
calculations described in note b. However, actual variations in CO2 emissions may be as low as ±10%, based on highest and lowest
industrial net carbon anode consumption values reported in (Cai et al. 2018), converted by mass balance to CO2. Therefore, where
possible, development and use of Tier 3 emission factors is encouraged.
c

25 A difference of only -4% / +8% in CO emission factors was estimated across different rare earth metals (from La to Gd
2metal, using Nd metal as a base case), when evaluating CO2 emissions by first principles (refer to note ‘b’ in Table 4.26).
This is due to due to the similarities in atomic mass for these rare earth metals.

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Tier 3 method for CO 2 emissions
Table 4.27 lists the facility-specific activity data (and uncertainties) at individual facilities, for use in Equation
4.36. The most significant factors in Equation 4.36 are metal production and net anode consumption for each RE
metal or alloy type i. Both these parameters should be collected from individual operating facilities for use with
Tier 3. The other compositional terms in the equation make minor adjustments for non-carbon components of theanodes (e.g. sulphur and ash, expected to be <3 percent wt) and thus are not as critical. Tier 3 is based on the useof specific operating facility data for these minor components. Carbon consumed per tonne of metal produced istypically recorded by rare earth production facilities given its economic significance; facilities refer to this as ‘net
anode consumption’ or ‘net carbon consumption’.
TABLE 4.27 (NEW)DATA SOURCES AND UNCERTAINTIES FOR PARAMETERS USED IN TIER 3 METHOD FOR CO2 EMISSIONS FROM ANODECONSUMPTION

Parameter

Data Source

Uncertainty(±%)

MPi: total metal production for RE
metal type i (tonnes metal per year)

Individual facility records±10% aNACi: net anode consumption per
tonne of RE metal type i (tonnes per
tonne metal)

Individual facility records±10% b

Impa: total non-carbon impurity
content in baked anodes (wt %) c

Individual facility records±10% bSource:Uncertainties in facility specific metal production records are expected to be low (i.e. ±10%, based on expert judgement). However note
(Vogel & Friedrich 2018) estimates an uncertainty of up to ±40% (±15,000 tonnes) for the 35,000 tonnes estimated global RE metal
production by fluoride electrolysis in 2015, due to unreported / illegal production of RE metals (Kingsnorth 2015).

ab
Uncertainties for CO2 based on facility specific information (apart from metal production) have been estimated based on expert
judgement, using uncertainty factors similar to those applied in the primary aluminium sector (sub-chapter 4.4, Table 4.11: uncertainties
for Tier 3 method for CO2 emissions from prebake cells).
c

Non-carbon impurities can include sulphur, ash, etc.

4.8.2.3

C HOICE OF METHOD FOR PFC S

During electrolysis of a RE metal, rare earth oxides (REOs) are dissolved in a fluoride melt comprising of rareearth fluorides (RExFy) and lithium fluoride (LiF). An example melt composition for Nd metal production is 85
percent wt NdF3, 10 percent LiF and 5 percent Nd2O3.
Perfluorocarbons (mainly CF4 and C2F6 – collectively referred to as PFCs) are formed from the reaction of the
carbon anode with the fluoride melt (e.g. NdF3 or DyF3) during a process upset condition known as an ‘anodeeffect’. This occurs when the concentration of dissolved REO in the electrolyte is too low to completely support
the standard anode reaction (normally producing RE metal and CO/CO2 gases), enabling additional anode reactions
that form PFC gases (Vogel et al. 2017; Cai et al. 2018; Kjos et al. 2018; Zhang et al. 2018). In addition to CF4
and C2F6, other PFCs reported by Cai et al. (2018) during RE metal production included: very low levels of C3F8(<1 percent total PFCs) and trace levels of c-C4F8 and C4F10 (<0.05 percent total PFCs). However, quantificationof these PFCs (other than CF4 and C2F6) in industrial measurements is extremely challenging and often impractical,
given the extremely low detection limits required.

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BOX 4.4 (NEW)ANODE EFFECT DESCRIPTION (FOR RARE EARTH METAL PRODUCTION BY FLUORIDE ELECTROLYSIS)An ‘anode effect’ is a process upset condition where an insufficient amount of rare earth oxide isdissolved in the electrolyte, resulting in the emission of PFC-containing gases and causing voltage
to be elevated above normal operating range. However, PFC generation might also occur in theabsence of detectable changes in voltage (Vogel et al. 2017; Kjos et al. 2018).
Unlike the analogous primary aluminium industry (refer to Box 4.2), many rare earth technologies
currently do not use automated computer control systems to detect anode effects, for example using
an elevated voltage threshold. As such, facility-specific activity data (e.g. anode effect performancedata) is often not available to estimate PFC emissions.
Due to reported differences in emissions profile (Cai et al. 2018; Zhang et al. 2018), PFC emissions can be
estimated separately for two groups of rare earth metals and alloys:•

Rare earth-iron (RE-Fe) alloys 26 with high melting-point (>1300°C) rare earth elements, e.g. Dy-Fe, Gd-Fe
and Ho-Fe;•

All other rare earth (Other-RE) metals/alloys including single and mixed rare earth metals, e.g. Nd, La, PrNd, etc.

In choosing a method for PFC emissions, it should be noted that the uncertainty associated with the Tier 3
methodology is significantly lower than for Tier 1; therefore it is good practice to use Tier 3 methodologies if thisis a key category. However, a pre-requisite for the Tier 3 method is the availability of facility-specific emission
factors, obtained through individual facility measurements. While no good practice guidance currently exists on
the measurement of PFCs and obtaining Tier 3 emission factors for the rare earth industry, the US EPA and IAI
protocols for measurement of PFCs in the aluminium smelting industry provide good analogous references(International Aluminium Institute 2006; US Environmental Protection Agency & International Aluminium
Institute 2008).
The decision tree in Figure 4.18 describes good practice in choosing the PFC inventory methodology appropriate
for national circumstances. The Tier 3 approach is preferred because plant-specific emission factors will lead toestimates that are more accurate. If no PFC measurements have been made to establish Tier 3 plant-specificemission factors, the Tier 1 method can be used until measurements have been made. Countries can use acombination of Tier 1 and Tier 3 depending on whether plant-specific emission factors are available fromindividual facilities.
Note that while the fundamental mechanisms that generate PFCs and anode effects in the rare earths industry are
similar to those in primary aluminium production (refer to sub-chapter 4.4), the lack of automation currently foundin the rare earths industry prevents the use of facility-specific activity data (e.g. using anode effect performancedata as per Tier 2 and 3 methods for PFC accounting in primary aluminium production) as a more accurate
methodology for estimating PFCs. Therefore, higher Tier 2 and 3 methods using process performance statistics oractivity data have not been included in these guidelines 27.
While rare earths production currently has a lower level of automation and process control compared to primaryaluminium production (see sub-chapter 4.4), the industry is still very much under development. There is ongoing
research to develop industrial technologies that can minimise PFC emissions (e.g. employing automation to ensure
control of REO concentrations) (Vogel & Friedrich 2017; Martinez et al. 2018). However, due to the scarcity of
published information on industrial emissions, separate PFC emission factors have not been provided for thesetechnologies.
Given the potential for further development within the industry, it is good practice to establish Tier 3 plant-specificemission factors for individual facilities where significant technology development and/or adoption of automated26

This category of RE-Fe alloys represented <5% of total rare earth metals/alloys produced by electrolysis in 2016 (expert
opinion). Due to their high melting point, these RE elements are typically produced using an alloying cathode (e.g. Fe) toform a liquid metal product, at higher operating cell voltage (compared to cells for all other RE metals/alloys in similar
conditions). The higher operating temperature and cell voltage increases the risk of PFC generation and is thought to be oneof the reasons behind the greater PFC emissions measured (expert opinion; Cai et al. 2018; Zhang et al. 2018).

27

Accounting of PFCs using activity data - such as anode effect performance statistics - in the rare earths industry is possible.
However this requires the industry to first have consistent definitions of anode effect performance, i.e. how to define thestart/end of an anode effect to determine the frequency and the duration of anode effects. Secondly, the level of automationin rare earth facilities must be sufficiently high to ensure accurate and consistent records these anode effect performancestatistics, a condition that does not currently reflect the majority of the rare earths industry.

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control systems have taken place. Finally, it is good practice to check the EFDB as a source for future PFC
emission factors for rare earths production.

Figure 4.18 (New)

Decision tree for calculation of PFC emissions from primary rare earth(RE) metal production

Start

Are facility specific
PFC emission factors
available per goodpractice 1?

Calculate PFC emissions
using Tier 3

Yes

Box 2: Tier 3

No
Is this a key
category2?

No

Is RE metal
production data
available 3?

Yes

No

Measure emission factors
for Tier 3 calculations

Estimate annual RE metal
production

Yes

Calculate PFC emissions
using Tier 1
Box 1: Tier 1

Notes:
1. While good practice guidelines for obtaining facility specific PFC emission factors from rare earth production facilities are currently notavailable, the IAI and US EPA/IAI greenhouse gas protocols for aluminium smelters are useful references due to the many similarities between
primary aluminium and rare earth smelting using fluoride-salts (International Aluminium Institute 2006; US Environmental Protection Agency& International Aluminium Institute 2008).
2. For discussion of key categories and use of decision trees, see Volume 1, Chapter 4, Methodological Choice and Identification of Key
Categories (noting Section 4.1.2 on limited resources).
3. For Tier 1 PFC emissions calculation, the production data requires differentiation of (a) rare-earth iron (RE-Fe) alloys, e.g. Dy-Fe and (b)all other rare earth (Other-RE) metals/alloys, e.g. Nd, Pr-Nd and La. However, there is no need for further differentiation as to the specificrare earth metal/alloy produced, or type of rare earth cell technology used at each facility.
4. This decision tree only provides a two-tiered methodology: Tier 1 using default emission factors, Tier 3 using facility-specific emission
factors. Additional Tier 2-3 methods using anode effect activity data to estimate PFC emissions (similar to the Tier 2-3 methods in the PFC
decision tree for aluminium production, sub-chapter 4.4.2.3) has not been provided, due to the lack of available activity data.

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Tier 1 and Tier 3 method for PFCs – by production
Both Tier 1 and Tier 3 methods for calculating PFCs employ emission factors that are based on metal production.
Methods are provided for CF4 and C2F6 gases since these are the major PFCs generated. C3F8 is also included forsake of completeness, however it is a very minor component of PFCs generated in rare earths (<1 percent total
PFCs) and it can be challenging or impractical to quantify from industrial facilities (if obtaining Tier 3 facilityspecific emission factors), given the extremely low detection limits required. Estimation of all other PFCs arebeyond the scope of this method as they are not significant (Cai et al. 2018).
The Tier 1 method uses default emission factors based on industrial measurements. PFC emissions can becalculated according to Equation 4.37, where emission factors for CF4, C2F6 and C3F8 gases are default emission
factors (refer to Table 4.28). The level of uncertainty in the Tier 1 methodology is greater because individual
facility emissions performance 28 is not taken into account. Note that some researchers (Vogel & Friedrich 2018)
have estimated PFC emission factors two to three-orders of magnitude greater than the default values given in
Table 4.28. These higher values were not used here because they were not measured, but modelled based on amass balance of NdF3 inputs to replace consumed fluorides, with the unlikely assumption that all consumed
fluorides are due to PFC generation. Nevertheless, they do indicate that the PFC emission factors from somefacilities may be higher than the Tier 1 factors presented here. Therefore, where possible, development and use ofTier 3 facility-specific PFC emission factors is encouraged.
Note that Equation 4.37 enables calculation of PFC emissions by individual RE metal/alloy produced. However
default emission factors are only available for two generic types of metals/alloys: (i) rare earth-iron alloys (e.g.
Dy-Fe) and (ii) all other rare earth metals/alloys (e.g. Nd, Pr-Nd), rather than all possible combinations of RE
metals / alloys due to the scarcity of published industrial emissions data 29. RE-Fe alloys were reported to havegreater PFC emissions than other RE metals (Cai et al. 2018; Zhang et al. 2018), consistent with the greater riskof PFC generation expected with the higher temperature and cell voltage operation required. Therefore, two default
Tier 1 emission factors for RE metals have been provided in these guidelines (Table 4.28). Hence, Equation 4.37
can be used with differentiation of RE metal production into these two metal/alloy types; further differentiation
into specific RE metals/alloys is not required.

EQUATION 4.37 (NEW)PFC EMISSIONS FROM RARE EARTH METALS PRODUCTION (TIER 1 AND TIER 3)

ECF4=∑ [( EFi

CF4 , i/1000) • MPi ]and=EC2 F6∑ [( EFi

C2 F6 , i/1000) • MPi ]andEC3 F8=∑ [( EFi

C3 F8 , i/1000) • MPi ]Where:ECF4= Emissions of CF4 from RE metal production, kg CF4

EC2F6= Emissions of C2F6 from RE metal production, kg C2F6

EC3F8

= Emissions of C3F8 from RE metal production, kg C3F8

EFCF4, i= Emission factor by RE metal i for CF4, g CF4/tonne RE metal

EFC2F6, i= Emission factor by RE metal i for C2F6, g C2F6/tonne RE metal

EFC3F8, i= Emission factor by RE metal i for C3F8, g C3F8/tonne RE metal

MPi= Metal production by RE metal i, tonnes RE metal

28

PFC emissions performance is impacted by technology, operating conditions and the anode effect performance of individual
facilities. While anode effect performance data from facilities are used to directly estimate PFCs in the analogous aluminium
smelting industry (refer to section 4.4.2.3), a similar method for rare earths has not been provided due to a lack of supporting
data that characterises emissions according to process statistics, such as anode effect performance.

29

While Tier 1 default emission factors are not available for all individual RE metal/alloy types, Equation 4.37 provides atemplate for the future (when such factors might become available) and for potential use in Tier 3 calculations.

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The Tier 3 method uses facility-specific emission factors in place of Tier 1 default emission factors. Facilityspecific emission factors are calculated from direct PFC measurement data at the individual facility (either
continuous or periodic measurements) and are obtained using established measurement practices and protocols –refer to analogues guidelines for the aluminium industry (International Aluminium Institute 2006; US
Environmental Protection Agency & International Aluminium Institute 2008)). It is good practice to use the Tier
3 method to estimate PFCs from rare earths when that is a key category.
For Tier 3, if facility-specific emission factors and production data are available for individual RE metals andalloys, then Equation 4.37 can be employed to calculate differentiated PFC emissions for each RE metal/alloy;
total PFC emissions can be obtained via the summation of these differentiated emissions. However, if
differentiated emission factors and production data by RE metal/alloy are unavailable, it is acceptable to use
Equation 4.37 without differentiation of RE metals/alloys produced.
Given the practical challenges in quantifying very low levels of C3F8, if a Tier-3 facility-specific emission factor
cannot be determined, it is possible to use a hybrid Tier 1-Tier 3 approach (i.e. Tier 1 emission factor for C3F8;
Tier 3 emission factors for CF4 and C2F6).

4.8.2.4

C HOICE OF EMISSION FACTORS FOR PFC S

Tier 1: Default emission factors for PFCs
Default emission factors for the Tier 1 method of estimating PFC emissions from rare earth metal production areprovided in Table 4.28, for use in Equation 4.37.
TABLE 4.28 (NEW)
TIER 1 DEFAULT EMISSION FACTORS AND UNCERTAINTY RANGES FOR THE CALCULATION OF PFC EMISSIONS FROM RARE
EARTH PRODUCTION

CF4
Rare Earth
Metal, i

C2F6

C3F8

EFCF4
(g/tonne RE
metal)

Uncertainty
Range c(+/-%)

EFC2F6(g/tonne RE
metal)

Uncertainty
Range c(+/-%)

EFC3F8(g/tonne RE
metal)

Uncertainty
Range c(+/-%)

RE-iron alloys(Dy-Fe, etc) a

146.1+/- 99%14.6+/- 99%0.05+/- 99%Other-RE
metals/alloys(Nd, Pr-Nd,
La, etc) b

35.8-54% / +30%

5.2

-95% / +108%

0.21-52% / +30%

Sources:a
For rare earth-iron (RE-Fe) alloys, CF4 default emission factors is based on the average of industrial measurements from production of
Dy-Fe alloy (1 cell, two measurements from the same facility) in China (Cai et al. 2018; Zhang et al. 2018). Note that the (Zhang et al.
2018) value of 106 g CF4/tonne RE metal was corrected by dividing out the 57.97% gas collection efficiency measured at the facility by(Cai et al. 2018). C2F6 and C3F8 default emission factors were calculated using the CF4 default factor, multiplied by the respective
C2F6/CF4 and C3F8/CF4 ratio measured by (Cai et al. 2018) for Dy-Fe production. Given that default factors are based on only two data
points, a higher uncertainty bound +/-99% has been estimated (expert opinion) rather than using the lowest/highest reported emission
values.

For all other rare earth (Other-RE) metals/alloys, CF4 default emission factors is based on the average of industrial measurements fromproduction of: (i) Nd metal (16 cells, one facility) (Zhang et al. 2018), with the value of 26.9 g CF4/tonne metal corrected by dividing out
the 57.97% gas collection efficiency measured at the facility by (Cai et al. 2018) and (ii) Pr-Nd alloy (15 cells, 6 cells in two facilities)
and La metal (6 cells, one facility) in China (Cai et al. 2018). C2F6 and C3F8 default emission factors were calculated using the CF4
default factor, multiplied by the average C2F6/CF4 and C3F8/CF4 ratio, respectively, measured by (Cai et al. 2018) from Pr-Nd alloy (15cells, 6 cells) and La metal (6 cells) production. The uncertainty range is estimated from the lowest/highest emission values from bothindustrial studies.
bNote that the default factors and uncertainty ranges here have been estimated with very limited sources of measured industrial data.
Some researchers (Vogel & Friedrich 2018) have estimated PFC emission factors two to three-orders of magnitude greater than thedefault values in this table (modelled ‘medium-emissions’ scenario for Nd production, based on mass balance of NdF3 inputs to replaceconsumed fluorides, but with the unlikely assumption that all consumed fluorides are due to PFC generation). Therefore where possible,
development and use of Tier 3 facility-specific PFC emission factors is encouraged.
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Tier 3: Facility-specific emission factors for PFCs
The Tier 3 facility-specific emission factors (and uncertainties), determined through direct PFC measurements at
individual facilities is listed in Table 4.29, for use in Equation 4.37.
TABLE 4.29 (NEW)DATA SOURCES AND UNCERTAINTIES FOR PARAMETERS USED IN TIER 3 METHOD FOR PFC EMISSIONSParameter

Data Source

Uncertainty(+/-%)

EFCF4: CF4 emission factor for metal
type i (kg CF4/tonne RE metal)

Individual facility records±10% aEFC2F6: C2F6 emission factor for
metal type i (kg C2F6/tonne RE
metal)

Individual facility records±10% aEFC3F8: C3F8 emission factor for
metal type i (kg C3F8/tonne RE
metal)

Individual facility records±35% aMPi: metal production for RE metal
type i (tonnes metal per year)

Individual facility records±10% bSource:Uncertainties for facility-specific emission factors have been derived from estimated sampling and gas analysis uncertainties during
direct industrial measurement of PFCs in rare earth facilities (Cai et al. 2018). Uncertainties for C2F6 and especially C3F8 can be higher,
particularly when concentrations are close to detection limits of gas measurement systems. Determination of Tier 3 facility-specificemission factors for C3F8 can be challenging and impractical, given the very low detection limits required to quantify these low-levelemissions. It is possible therefore to use a hybrid Tier 1-Tier 3, where C3F8 emissions are estimated using Tier 1 default factors, and CF4
and C2F6 using Tier 3, respectively.

ab
Uncertainties in facility specific metal production records are expected to be low (i.e. ±10%, based on expert opinion). However (Vogel& Friedrich 2018) estimates an uncertainty of up to +40% (+15,000 tonnes) for the 35,000 tonnes estimated global RE metal production
by fluoride electrolysis in 2015, due to unreported / illegal production of RE metals (Kingsnorth 2015).

4.8.2.5

C HOICE OF ACTIVITY DATA AND EMISSION FACTORS

Production statistics should be available from every facility to enable use of the Tier 1 methods for both CO2 andPFC emissions. Therefore, uncertainty in the tonnes of rare earth metals and alloys produced is likely to be low inmost countries that have good reporting systems (±10 percent uncertainty, based on expert judgement); othersources (Vogel & Friedrich 2018) estimate up to +40 percent uncertainty in global RE metal production (in 2015)
due to the presence of unreported or illegal RE metal production in some parts of the world.
For PFC emissions, it is good practice to use Tier 3 facility-specific emission factors for individual facilities,
where reliable measurements have been taken to establish facility-specific emission factors (i.e. using a method
similar to that in the USEPA/IAI Protocol for Measurement of CF4 and C2F6 emissions from Primary Aluminium
Production, 2008).
For CO2 emissions, it is also good practice to collect data to support Tier 3 methods, which requires facility specificinformation on anode consumption and anode composition to calculate CO2 emissions.

4.8.2.6

C OMPLETENESS

Completeness for this source category requires accounting for both CO2 and PFC emissions during the productionof rare earth metals. Primary RE metal production facilities (by fluoride-electrolysis of REOs) are expected tohave the information required for these estimates, including records of the tonnes of RE metals produced (bothtotal and by individual RE metal/alloy types) throughout the entire time series covered by the inventory. In addition,
anode consumption data are expected to be available over the same period. Primary RE production (by fluorideelectrolysis of REOs) also utilizes a high intensity of electricity (per tonne of RE metal); however carbon dioxide
emissions associated with electricity input are covered separately under Volume 2: Energy.
Completeness also requires that all rare earth metals production and/or all rare earth metal producers in the country
be identified. As noted above, some sources have estimated that global RE metal production may have been
underestimated by 40 percent in 2015 due to unreported or illegal RE metal production in some parts of the world(Vogel & Friedrich 2018).

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Chapter 4: Metal Industry Emissions

4.8.2.7

D EVELOPING A CONSISTENT TIME SERIES

Rare earth metal/alloy production statistics should be available for the entire history of the facility.
Developing a consistent time series for CO2 emissions should not be a problem since it is expected that mostfacilities have measured and recorded activity data for anode consumption and composition. Where historic anodeconsumption and compositional data are missing, carbon dioxide emissions can be estimated from RE metal
production utilizing the Tier 1 method.
Developing a consistent time series for PFC emissions should also be reasonably straightforward as both Tier 1
and 3 methods utilise metal production statistics to estimate emissions. Backcasting of Tier 3 methods is preferredover the use of Tier 1 emission factors. Because PFC emissions have only recently become a focus area of the rareearths industry, the majority of facilities do not have further activity data to support any other methodologies (e.g.
process-data on anode effect performance as per the primary aluminium industry, sub-chapter 4.4.2.3).
It is good practice to consult with representatives from the operating facilities, either directly or through regional,
national or international organizations representing the rare earths industry to develop the best strategy for the
specific group of operating locations included in the national inventory.

4.8.3

Uncertainty assessment

There are major differences in the uncertainty for PFC emissions depending on the choice of Tier 1 or Tier 3
methods. The differences in uncertainty resulting from the choice of Tier 1 or Tier 3 methods for CO2 emissions
is smaller, but still significant.

4.8.3.1

E MISSION FACTOR UNCERTAINTIES

Uncertainties in CO 2 emission factors
For CO2 emissions, there are major differences in the uncertainty of emissions depending on the choice of Tier 1
or 3 methods. The overall uncertainty in calculating CO2 emissions from carbon anode consumption for Tier 3
should be less than ±20 percent, and less than ±30 percent for Tier 1. While Tier 1 default emission factors arecalculated using the same first principles as Tier 3 (mass-balance assuming all carbon content in the net anodeconsumed is emitted as CO2), there are assumptions for Tier 1 which increases the level of uncertainty. These
include: (i) an assumed net anode consumption and (ii) assuming zero non-carbon impurities, i.e. 100 percent of
net anode consumed is in the form of carbon. The use of facility-specific net anode consumption and anodecompositional data in the Tier 3 method removes the need for these assumptions, leading to lower uncertainty incalculating CO2 using Tier 3. This is because the reactions leading to carbon dioxide emissions is reasonably wellunderstood and the emissions are very directly connected to the tonnes of RE metal produced through fundamental
electrochemical equations for REO reduction at the carbon anode and oxidation from thermal processes. Boththese processes are taken into account when calculating CO2 using net anode consumption and anodecompositional data.

Uncertainties in PFC emission factors
For PFC emissions, there are major reductions in uncertainty when choosing the Tier 3 over the Tier 1 method.
The high level of uncertainty in the Tier 1 method results from the default emission factors being based on only
two sets of industrial PFC measurements from rare earth facilities (Cai et al. 2018; Zhang et al. 2018). Due to thelimited number of industrial measurements, there is no differentiation of Tier 1 default emission factors fordifferent rare earth metals and production technologies, apart from the two generic metal/alloy types: (i) rare earthiron (RE-Fe) alloys and (ii) all other rare earth (Other-RE) metals/alloys. In order to achieve lower uncertainty
using Tier 3 PFC calculations, it is important to use good practices in making facility specific PFC measurements.
Measurement good practices have been established for the aluminium industry in a protocol available globally(International Aluminium Institute 2006; US Environmental Protection Agency & International Aluminium
Institute 2008); due to the similarities between the industries, these are recommended as a guiding reference formeasurements in the rare earths industry, until a RE industry-specific protocol or guideline is established. When
properly obtained, the Tier 3 coefficients will have an uncertainty of ±10 percent for CF4 and C2F6 and ±35 percent
for C3F8 at the time coefficients are measured (Cai et al. 2018).

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4.8.3.2

A CTIVITY DATA UNCERTAINTIESWhile uncertainties in annual production data for RE metals should be minor (less than ±10 percent), there aresome reports of unreported/illegal production in parts of the world that amount to ±40 percent of estimated global
metal production in 2015 (Kingsnorth 2015; Vogel & Friedrich 2018). The uncertainty in recorded carbon anodeconsumption is estimated to be low (less than ±10 percent).

4.8.4
4.8.4.1

Quality Assurance/Quality Control (QA/QC),
Reporting and Documentation
Q UALITY A SSURANCE /Q UALITY C ONTROL (QA/QC)

It is good practice at all primary rare earth metal production facilities to maintain records of all the necessary
activity data to support calculations of emission factors as suggested in these guidelines. These records will include
production of rare earth metals (ideally by RE metal/alloy type and by RE technology type) and consumption ofcarbon materials used. It is good practice to aggregate emission estimates from each smelter to estimate total
national emissions. However, if smelter-level production data is unavailable, smelter capacity data may be usedalong with aggregate national production to estimate smelter production.
It is good practice to verify facility CO2 emission factors per tonne of RE metal by comparison with the expected
range of variation that would be predicted from the variation noted in Table 4.26 for CO2 specific emissions.
Similarly, facility-specific PFC emission factors per tonne RE metal should be compared with the expected rangeof variation noted in Table 4.28. It is suggested that any inventory value outside the expected range of variation
be confirmed with the data source.
Use of standard measurement methods improves the consistency of the resulting data and knowledge of thestatistical properties of the data. Until a rare earths industry-specific guideline or protocol has been established,
the US EPA ‘Protocol for Measurement of Tetrafluoromethane (CF4) and Hexafluoroethane (C2F6) Emissions
from Primary Aluminum Production’ (US Environmental Protection Agency & International Aluminium Institute2008) is an internationally recognized standard and can be used as a guidance document for obtaining PFC
emission factors for a rare earths facility, given the similarities between aluminium and rare earths fluorideelectrolysis processes 30. It is good practice to encourage plants to use this method for developing Tier 3 PFC
emission factors. Significant differences between calculated coefficients based on PFC measurements and theindustry average Tier 1 emission factors should elicit further review and checks on calculations. Large differences
should be explained and documented.
Inter-annual changes in emissions of carbon dioxide per tonne RE metal are not likely to exceed ± 20 percent 31
based on the consistency of the underlying processes that produce carbon dioxide. In contrast, inter-annual changes
in emissions of PFCs per tonne of RE metal may change by values as much as ±100 percent 32. Increases in PFC
specific emissions can result from process instability or major changes in process conditions, such as unforeseen
power interruptions, changes in sources of REO feed materials, cell operational problems, and changes inamperage to increase RE metal production. Decreases in PFC specific emissions can result from upgrades in cell
technology such as increasing automation, installation of equipment to continuously feed REO, improved work
practices and better control of raw materials.

30

Note that unlike the aluminium industry, the Tier 3 methodology for rare earths estimates PFCs using production-based
emission factors only. The method does not consider more detailed process data, such as anode effect coefficients andperformance data (as per the Tier 2-3 methodology for accounting PFCs from aluminium in sub-chapter 4.4), due to a lackof published data to support it.

31 Inter-annual variations in CO emissions in the analogous aluminium industry (sub-chapter 4.4) typically do not vary more
2than ± 10%; however, given the scarcity of published data, greater variations (i.e. ± 20%) might be allowed for in the rareearth industry.

32 Inter-annual variations in PFC emissions in the analogous aluminium industry (sub-chapter 4.4) typically do not vary morethan ± 100%; a similar level of variations might be expected in the rare earth industry, as supported by reductions in measured
emissions over time in one facility (Cai et al. 2018).

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Chapter 4: Metal Industry Emissions

4.8.4.2

R EPORTING AND D OCUMENTATION

It is good practice to document and archive all information required to produce the national emissions inventory
estimates as outlined in Volume 1, Chapter 6, Quality Assurance and Quality Control, Internal Documentation andArchiving. Some examples of specific documentation and reporting relevant to this source category are provided
below.
It is not practical to include all documentation in the national inventory report. However, the inventory should
include summaries of methods used and references to source data such that the reported emissions estimates aretransparent and steps in their calculation may be retraced. To improve transparency, it is good practice to reportemissions for PFCs from rare earths production separately from other source categories. Additionally, it is goodpractice that CF4, C2F6 and C3F8 emissions are reported separately on a mass basis.
The supporting information necessary to ensure transparency in reported emissions estimates is shown in Table
4.30 below.
Much of the production and process data are considered proprietary by operators, especially where there is only
one smelter in a country. It is good practice to exercise appropriate techniques, including aggregation of data, toensure protection of confidential data.
TABLE 4.30 (NEW)GOOD PRACTICE REPORTING INFORMATION FOR CALCULATING CO2 AND PFC EMISSIONS FROM RARE EARTH METALPRODUCTION BY TIER
Data

Tier 1

Tier 3CO2 emissions
Annual national production (by metal and alloy type)X

Annual production by facility (by metal and alloy type)X

Net anode consumption

X

Anode composition / impurityX

PFC emissions (CF4, C2F6 and C3F8 reported separately on mass basis)
Annual national production (by metal/alloy type)X

Annual production by facility (by metal/alloy type)
Default technology emission coefficients

X
X

Facility-specific emission coefficients
Supporting documentation

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X
X

X

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Volume 3: Industrial Processes and Product Use

REFERENCESSECTION 4.2
References newly cited in the 2019 Refinement

EU IPPC BREF (2013). Best Available Techniques (BAT) Reference Document for Iron and Steel Production,
Industrial Emissions Directive 2010/75/EU (Integrated Pollution Prevention and Control), Rainer Remus,
Miguel A. Aguado-Monsonet. Serge Roudier, Luis Delgado Sancho, JRC Reference Report, 2013,
available at http://eippcb.jrc.ec.europa.eu/reference/BREF/IS_Adopted_03_2012.pdf.
Fruehan, R.J., Fortini, O., Paxton, H.W., & Brindle, R. (2000) Theoretical Minimum Energies To Produce Steelfor Selected Conditions. Prepared under contract to Energetics, Inc. Columbia, MD For the U.S.
Department of Energy Office of Industrial Technologies Washington., DC Carnegie Mellon University
Pittsburgh,
PA,
March
2000,
availableathttps://www.energy.gov/sites/prod/files/2013/11/f4/theoretical_minimum_energies.pdf
International Organization for Standardization (ISO). (2013a) ISO 14404-1:2013 - Calculation method of carbon
dioxide emission intensity from iron and steel production - Part 1: Steel plant with blast furnace. Available
at https://www.iso.org/standard/57298.html .
International Organization for Standardization (ISO). (2013b) ISO 14404-2:2013 - Calculation method of carbon
dioxide emission intensity from iron and steel production - Part 2: Steel plant with electric arc furnace(EAF). Available at https://www.iso.org/standard/57299.html
Japan NIR 2018: National Greenhouse Gas Inventory Report of Japan (2018), Greenhouse Gas Inventory Officeof Japan (GIO), Center for Global Environmental Research (CGER) & National Institute for Environmental
Studies (NIES). (2018) Available at: http://www-gio.nies.go.jp/aboutghg/nir/2018/NIR-JPN-2018v4.1_web.pdf
Official Journal of the European Union. (2011) Commission Decision of 27 April 2011 determining transitional
Union-wide rules for harmonised free allocation of emission allowances pursuant to Article 10a of Directive
2003/87/EC of the European Parliament and of the Council.
U.S. Code of Federal Regulations (CFR). (2018) Title 40: Protection of Environment, Part 98 - Mandatory
greenhouse gas reporting, Subpart C - General Stationary Fuel Combustion Sources, §98.33 Calculating
GHG emissions, U.S. Environmental Protection Agency, available at: https://www.ecfr.gov/cgi-bin/textidx?SID=921a214b1daec4eb768bb5caead0dbaa&mc=true&node=se40.23.98_133&rgn=div8
U.S. Environmental Protection Agency (2012). Available and Emerging Technologies for Reducing Greenhouse
Gas Emissions from the Iron and Steel Industry Prepared by the Sector Policies and Programs Division,
Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, September 2012,
available at: https://www.epa.gov/sites/production/files/2015-12/documents/ironsteel.pdf .
Zhang, X., Wu, G.,Wu, S. & Xiang, X. (2012) Determination of carbon dioxide emission factors in typical
processes for large iron-steel companies. Acta Scientiae Circumstantiae 42(8): 2024-2027, available at
http://www.actasc.cn/hjkxxb/ch/reader/create_pdf.aspx?file_no=20111012001 .

References copied from the 2006 IPCC Guidelines

EEA (2005). EMEP/CORINAIR. Emission Inventory Guidebook – 2005, European Environment Agency,
Technical report No 30. Copenhagen, Denmark, (December 2005). Available from web site see:
http://reports.eea.eu.int/EMEPCORINAIR4/en
International Iron and Steel Institute (2004). Steel Statistical Yearbook 2004: International Iron and Steel Institute,
COMMITTEE ON ECONOMIC STUDIES, Brussels.
IPPC (2001). Integrated Pollution Prevention and Control (IPPC), Best Available Techniques Reference Documentonthe
Production
of
Iron
and
Steel,
December
2001,
availableat
http://eippcb.jrc.ec.europa.eu/reference/BREF/isp_bref_1201.pdf.
Schoenberger, H. (2000). European Conference on “The Sevilla Process: A Driver for Environmental Performancein Industry” Stuttgart, 6 and 7 April 2000, BREF on the Production of Iron and Steel - conclusion on BAT,
Dr. Harald Schoenberger, Regional State Governmental Office Freiburg, April 2000.

SECTION 4.4

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Chapter 4: Metal Industry Emissions

References newly cited in the 2019 Refinement

Aarhaug, T. A., Ferber, A., Gaertner, H., Kolas, S., Ryman, S. O. & P., G. (2018) Validation of Online Monitoringof PFC by QCL with FTIR Spectroscopy. In: TMS Light Metals, pp. 1487-1493. Phoenix.
Asheim, H., Aarhaug, T. A., Ferber, A., Kjos, O. S. & Haarberg, G. M. (2014) Monitoring of Low Cell Voltage
PFC Formation in 200 to 300 kA Aluminium Electrolysis Cells. In: 7th KIFEE, Kyoto.
Bardai, A., Aga, B. E., Berveling, A., Droste, C., Fechner, M., Haugland, E., Karlsen, M., Liane, M., Ryman, S.
O., Vee, T. H., Wedershoven, E. & Ovstetun, F. (2009) HAL 4e - Hydro's new generation cell technology. In:
TMS Light Metals, pp. 301-305.
Burkat, V. S., et al. (2018). Study of perfluorocarbon (PFC) emissions from vertical stud (VSS) self-baking anodecells during production of aluminium outside anode effects. Metallurgist.
Chen, X., Li, W., Zhang, Y., Qiu, S. & Bayliss, C. (2013) Investigation on formation mechanism of non-anodeeffect related PFC emissions from aluminum reduction cells. In: TMS Light Metals, pp. 877-881.
Coursol, P., Coulombe, P., Gosselin, S., Lavoie, D., Simard, J.-M., Marks, J., Fardeau, S. (2011) Impact ofOperations at Low Anode-cathode Distance on Energy Consumption and Greenhouse Gas Emissions at
Aluminerie Alouette JOM 63(8): 109-115.Dando, N., Xu, W. & Marks, J. (2009) Comparison of PFC
Emissions for Operation and Newly Started Pots at the ALCOA Fjardaal Point Fed Prebake Smelter. In: TMSLight Metals, ed. G. P. Bearne, pp. 269-273.
Dando, N. R., Menegazzo, N., Espinoza-Nava, L., Westendorf, N. & Batista, E. (2015) Non anode effects PFC :Measurement consideration and potential impact. In: Light Metals, pp. 551-555. Orlando.
Dando, N. R., Xu, W., Nichols, R., Rusche, S. & Nemie, M. (2008) Comparison of PFC Emission Rates forOperation and Newly Started Pots at a Horizontal Stud Soderberg Smelter. In: TMS Light Metals, ed. D.
DeYoung, pp. 233-237.
Dion, L., Gaboury, S., Picard, F., Kiss, L. I., Poncsak, S. & Morais, N. (2018a) Universal Approach to Estimate
Perfluorocarbons Emissions During Individual High-Voltage Anode Effect for Prebaked Cell Technologies.
JOM 70(9): 1887-1892.
Dion, L., Kiss, I. L., Poncsák, S. & Lagacé, C. L. (2016) Prediction of low voltage tetrafluoromethane emissions
based on the operating conditions of an aluminium electrolysis cell. JOM 68(9): 2472-2482.
Dion, L., Wong, D. S., Nunez, P., Gaboury, S. & Spirin, A. V. (2018b) Evaluation of time consistency whenquantifying emissions of perfluorocarbons resulting from low voltage anode effects. In: TMS Light Metals, pp.
1457-1462. Phoenix, AZ, USA.
Emirates
GlobalAluminium.
(2017)
Reduction
https://www.ega.ae/en/technology/reduction-cell-technologies/.

Cell

Technologies.

URL

Fraser, P., Steel, P. & Cooksey, M. (2013) PFC and Carbon Dioxide Emissions from an Australian Aluminium
Smelter using Time-Integrated Stack Sampling and GC-MS, GC-FID Analysis. In: TMS Light Metals, pp. 871876. San Antonio.
International Aluminium Institute. (2006) The Aluminium Sector Greenhouse Gas Protocol. 65 pages.
International Aluminium Institute. (2018) Current IAI statistics - Perfluorocarbons emissions.
Kalban A.J.M., Al Farsi Y.A.M., Binbrek A.S.S. (2013) Reduction Cell Technology Development at Dubal
Through 20 Years. Bearne G., Dupuis M., Tarcy G. (eds) In: Essential Readings in Light Metals: Aluminium
Reduction Technology. Wiley, pp. 494-499.Kristensen, W., Hoskuldsson, G. & Welch, B. J. (2007) Potline
startup with low anode effect frequency. In: Light Metals, pp. 712-717.
Maltais, J.-N., Ross, J., Marcoux, A. & Gaudreault, G. (2010) Application of a Method for the Determination of
PFC Emissions During Aluminium Pot Start-up. In: TMS Light Metals, pp. 271-276.
Marks, J. & Nunez, P. (2018a) New Algorithm for Calculating CF4 Emissions from High Voltage Anode Effects.
In: Light Metals, Phoenix.
Marks, J. & Nunez, P. (2018b) Updated Factors for Calculating PFC Emissions from Primary Aluminum
Production. In: TMS Light Metals, pp. 1519-1525. Phoenix, AZ.
Reny, P., Segatz, M., Leder, F.-M., Midtun, O. J., Hop, J. G. & Gikling, H. (2016) Low Energy Start-Up for Low
Energy Cells. In: International Committee for Study of Bauxite, Alumina & Aluminium, Quebec city.
Rio Tinto Alcan. (2013) AP Technology - Our products and services. URL https://www.aptechnology.com/SitePages/products.aspx.

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Tabereaux, A. (2004) Anode effects and PFC emissions rates. In: 8th australasian aluminium smelting technology
conference.
Tarcy, G. P., Kvande, H., & Tabereaux, A.(2011) Advancing the industrial aluminium process: 20th century
breakthrough inventions and developments. JOM 63(8): 101-108.
US Environmental Protection Agency & International Aluminium Institute. (2008) Protocol for Measurement of
Tetrafluoromethane (CF4) and Hexafluoroethane (C2F6) Emissions from Primary Aluminum Production. 42
pages.
Wong, D. & Marks, J. (2013) Continuous PFC emissions measured on individual 400 kA cells. In: Light Metals,
pp. 865-870. San Antonio.
Wong, D., Nunez, P., Chen, X., Cai, B. & Bo, X. (2018) PFCs from the Chinese Aluminium Sector—Challenges
in Emissions Accounting and Further Characteristics. In: TMS Light Metals, pp. 1527-1535. Phoenix.
Wong, D. S., Fraser, P., Lavoie, P. & Kim, J. (2015) PFC emissions from detected versus nondetected anodeeffects in the aluminium industry. JOM 67(2): 342-353.
Xu, W., Dando, N. & Sedlacek, D. (2008) Comparison of PFC Emission Coefficients for Operating and Startup
Pots at a Side Work Prebake Smelter. In: TMS Light Metals, ed. D. deYoung, pp. 245-248.
Zarouni, A. A., Reverdy, M., Zarouni, A. & Vankatasubramaniam, K. G. (2013) A study of low voltage PFC
emissions at DUBAL. In: Light Metals, pp. 859-863. San Antonio.

References copied from the 2006 IPCC Guidelines

IAI (2000). International Aluminium Institute, International Aluminium Institute (2000) ‘Life Cycle Assessmentof Aluminium’
IAI (2001). International Aluminium Institute, Perfluorocarbon Emissions Reduction Programme 1990 - 2000,
2001, available at http://www.world-aluminium.org/iai/publications/documents/pfc2000.pdf.
IAI (2005a). International Aluminium Institute, The Aluminium Sector Greenhouse Gas Protocol,
http://www.world-aluminium.org/environment/climate/ghg_protocol.pdf, 2005.
IAI (2005b). International Aluminium Institute, survey on composition of production materials, 2005 (unpublished)
IAI (2005c). International Aluminium Institute, Annual Anode Effect Survey 2003, www.world-aluminium.org,
2005.
U.S. EPA and IAI (2003), U.S. Environmental Protection Agency and International Aluminium Institute,
USEPA/IAI Protocol for Measurement of PFCs from Primary Aluminium Production, EPA 43-R-03-006, May
2003.

SECTION 4.8
References newly cited in the 2019 Refinement

Cai, B., Liu, H., Kou, F., Yang, Y., Yao, B., Chen, X., Wong, D. S., Zhang, L., Li, J., Kuang, G., Chen, L., Zheng,J., Guan, D. & Shan, Y. (2018) Estimating perfluorocarbon emission factors for industrial rare earth metalelectrolysis. Resources, Conservation and Recycling 136: 315-323.
International Aluminium Institute. (2006) The Aluminium Sector Greenhouse Gas Protocol. 65 pages.
Kingsnorth, D. J. (2015) The Global Rare Earths Industry Today - Plagued by Illegal Production in China”. In:
11th International Rare Earths Conference, Singapore.
Kjos, O. S., Solheim, A., Aarhaug, T., Osen, K. S., Martinez, A. M., Sommerseth, C., Gudbrandsen, H., Støre, A.
& Gaertner, H. (2018) PFC Evolution Characteristics During Aluminium and Rare Earth Electrolysis. In: Light
Metals 2018, pp. 1449-1455.
Liu, K.-r., Chen, J.-s. & Wei, X.-j. (2001) Analysis of anodic gases in neodymium electrolysis. The Chinese
Journal of Nonferrous Metals 11(6): 1118-1120.
Martinez, A. M., Osen, K. S., Store, A., Gudbrandsen, H., Kjos, O. S., Solheim, A., Wang, Z., Oury, A. & Namy,P. (2018) Manufacturing of Dysprosium-Iron Alloys by Electrolysis in Fluoride-Based Electrolytes.
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