Methodological issues 4521 Choice of method

CO2 EMISSIONS FROM PRIMARY PRODUCTION

The choice of a good practice method for inventory preparation of carbon dioxide emissions from the primary magnesium (raw material) production segment will depend on national circumstances. The decision tree (see Figure 4.13, Decision Tree for Estimation of CO2 Emissions from Primary Magnesium Production) describes good practice in adapting the methods to these country-specific circumstances.

Tier 1

The Tier 1 method relies on national primary production data and knowledge of raw materials used in the country. National production data may not be publicly available as there are a limited number of countries producing magnesium and only a few individual producers - often only one in a country - often resulting in the designation of national production data as confidential. In the absence of national primary magnesium production statistics, industry associations, such as the International Magnesium Association (http://www.intlmag.org/), may be able to provide regional statistics. Failing other data, it may be possible to estimate primary magnesium production from annual national magnesium metal sales. This method has increased uncertainty, since it does not account for magnesium used in national product manufacturing.

CO2 emissions are calculated using Equation 4.28.

Equation 4.28

CO2 EMISSIONS FROM PRIMARY MAGNESIUM PRODUCTION (TIER 1)

Where:

ECO2 = CO2 emissions from primary magnesium production, Gg Pd = national primary magnesium production from dolomite, tonnes Pmg = national primary magnesium production from magnesite, tonnes

EFd = Default emission factor for CO2 emissions from primary magnesium production from dolomite, tonne CO2/tonne primary Mg produced

EFmg = Default emission factor for CO2 emissions from primary magnesium production from magnesite, tonne CO2/tonne primary Mg produced

Tier 2

The Tier 2 method for determining CO2 emissions from primary magnesium involves collecting company/plant-specific empirical emission factors, in addition to company specific production data. The company specific emission factors may differ substantially from the default emission factors depending on process materials handling. This collection should take place if the emissions are a key category.

CO2 emissions are calculated using Equation 4.29.

Equation 4.29

CO2 EMISSIONS FROM PRIMARY MAGNESIUM PRODUCTION (TIER 2)

Where:

ECO2 = CO2 emissions from primary magnesium production, Gg Pi = primary magnesium produced in plant i, tonne

EFi = company/plant-specific emission factor for CO2 emissions from primary magnesium production obtained from company/plant i, tonne CO2 /tonne primary Mg produced

Tier 3

If actual measured CO2 emissions data are available from individual primary magnesium facilities, these data can be aggregated and used directly to account for national emissions.

MAGNESIUM CASTING PROCESSES (PRIMARY & SECONDARY)

The choice of a good practice method for inventory preparation of SF6 emissions from magnesium casting process segment will also depend on national circumstances. The decision tree (Figure 4.14, Decision Tree for Estimation of SF6 Emissions from Magnesium Processing) describes good practice in adapting the methods to these country-specific circumstances.

Tier 1 - default emission factors

The Tier 1 method is based on the total amount of magnesium casting or handling in the country (Equation 4.30). The underlying assumption for the Tier 1 approach is that all SF6 consumption in the magnesium industry segment is emitted as SF6. As described in Section 4.5.1, this assumption will potentially overestimate the GHG emissions, but the overestimate will lie within the overall uncertainty range given in Section 4.5.3. The basic Tier 1 method uses a single value as a basis for the default emission calculation when SF6 is used for oxidation protection, despite the fact that SF6 consumption vary substantially between different casting operations and operators (sometimes orders of magnitude). The Tier 1 method should be used only when the inventory compiler has no knowledge of type of magnesium handling- or casting operation (recycling, billet casting or die-casting etc.)

Where

ESF6 = SF6 emissions from magnesium casting, tonnes

MGc = total amount of magnesium casting or handling in the country, tonnes

EFSF6 = default emission factor for SF6 emissions from magnesium casting, kg SF6/tonne Mg casting

Tier 2 - company-specific SF6 consumption

As for the Tier 1 method, the Tier 2 method also assumes that all SF6 consumed is subsequentlyemitted. Instead of the amount of magnesium casting, however, the Tier 2 method uses data on national (or sub-national) consumption of SF6 in the magnesium industry as reported by the industry or available through other sources such as national statistics (Equation 4.31).

The most accurate application of the method is normally collection of direct data on SF6 consumption from all individual users of the gas in the magnesium industry. If no direct data are available, an alternative but a less accurate method is to estimate the share of annual national SF6 consumption attributable to the magnesium industry. This requires collecting annual data on national SF6 sales and assumes that all SF6 gas sold to the magnesium industry is emitted within the year.

Where

ESF6 = SF6 emissions from magnesium casting, tonnes

CSF6 = consumption of SF6 in magnesium smelters and foundries, tonnes

Tier 3 - direct measurement approach

If actual measured emission data are available from individual magnesium processing facilities, these data can be aggregated and used directly to account for national emissions. In such reporting, it is good practice to include destruction of SF6 and formation of secondary gas products.

Figure 4.13 Decision tree for estimation of CO2 emissions from raw materials calcination in the primary magnesium production process

Figure 4.13 Decision tree for estimation of CO2 emissions from raw materials calcination in the primary magnesium production process

Policy Factors

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.

Figure 4.14 Decision tree for estimation of SF6 emissions from magnesium processing

Figure 4.14 Decision tree for estimation of SF6 emissions from magnesium processing

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.

HFC-134a, FK 5-1-12 and decomposition products (e.g., PFCs)

As described in Section 4.5.1, the industrial use of fluorinated compounds other than SF6 for magnesium oxidation protection commenced in 2003-2004. As such, the industrial experience in using these compounds for magnesium protection purposes is yet very limited. Even individual plants will have little historic data, if any, on actual emissions of these other fluorinated compounds from their operations. While there is a general sense in industry that the volume use of these alternate gases will be less than SF6, there are no data available at this time on which to base emission factors. Hence, it is not possible at this time to develop an emission factor-based approach (Tier 1 or 2) for reporting emissions.

However, if the GHG emission from the use of magnesium cover gases is a national key category, it is good practice to collect direct measurements or meaningful indirect measurements of GHG emissions (fugitive emissions of HFC134-a and FK 5-1-12 as well as emissions of PFCs as decomposition products) from magnesium foundries using HFC-134a or FK 5-1-12 as cover gases. This is consistent with the Tier 3 approach.

Carrier gases

The contribution of carbon dioxide carrier gas used in protective cover gas systems is normally a small fraction of the global warming potential. In general, these emissions may be disregarded.

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