TECHNICAL SUPPORT DOCUMENT FOR
PROCESS EMISSIONS FROM MAGNESIUM
PRODUCTION AND PROCESSING: PROPOSED
RULE FOR MANDATORY REPORTING OF
GREENHOUSE GASES
Climate Change Division
Office of Atmospheric Programs
U.S. Environmental Protection Agency
February 10,2009
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CONTENTS
1. Source Description 3
a. Total U.S. Emissions 3
2. Options for Reporting Threshold 3
3. Options for Monitoring Methods 5
a. Option 1: Default Emission Factor 5
b. Option2: Cover Gas Consumption 5
c. Option 3: Facility-specific measurements of emissions 6
4. Procedures for Estimating Missing Data 7
5. QA/QC Requirements 7
6. Reporting Procedures 7
7. References 8
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1. Source Description
Magnesium is a high-strength and light weight metal that is important for the manufacture of a wide range of
products and materials, such as electronics, vehicles, and other machinery. The United States accounts for less than
10 percent of world primary magnesium production (USGS 2007), but is a significant importer of magnesium for
casting operations. The production and processing of magnesium metal under common practice results in emissions
of sulfur hexafluoride (SF6).
The magnesium metal production (primary and secondary) and casting industry typically uses SF6 as a cover gas to
prevent the rapid oxidation and burning of molten magnesium in the presence of air. A dilute gaseous mixture of
SF6 with dry air and/or CO2 is blown over molten magnesium metal to induce and stabilize the formation of a
protective crust. A small portion of the SF6 reacts with the magnesium to form a thin molecular film of mostly
magnesium oxide and magnesium fluoride. The amount of SF6 reacting in magnesium production and processing is
under study but presently assumed to be negligible. Thus, all SF6 used is assumed to be emitted into the atmosphere.
Cover gas systems are typically used to protect the surface of a crucible of molten magnesium that is the source for a
casting operation and to protect the casting operation itself (e.g., ingot casting). Sulfur hexafluoride has been used
in this application around the world for the last twenty years. Due to increasing awareness of the global warming
potential of SF6, the magnesium industry has begun exploring climate-friendly alternative melt protection
technologies. At this time the leading alternatives are HFC-134a, a fluorinated ketone FK 5-1-12 (C3F7C(O)C2F5),
and dilute sulfur dioxide (SO2). The application of the fluorinated alternatives mentioned here may generate
byproduct emissions of concern including perfluorocarbons (PFCs).
a. Total U.S. Emissions
Emissions of SF6 from magnesium production and processing in the United States were estimated to be 3.2 million
metric tons of CO2 equivalent (MMTCO2e) in 2006 (EPA 2008). There are approximately 10 magnesium die
casting facilities in the United States which accounted for 29 percent, or 0.9 MMTCO2e of total magnesium-related
SF6 emissions. Primary and secondary production activities accounted for 64 percent of total emissions, or 2
MMTCO2e. Other smaller casting activities such as sand and permanent mold accounted for the remaining seven
percent of total magnesium-related emissions of SF6.
2. Options for Reporting Threshold
EPA evaluated a range of threshold options for magnesium production and processing facilities. These included
emission-based thresholds of 1,000, 10,000, 25,000 and 100,000 mtCO2e and capacity-based thresholds equivalent
to these. The capacity-based thresholds were based on 100-percent capacity utilization and an SF6 emission rate of
1.6 kg SF6/ metric ton of magnesium produced or processed. This emission factor represents the sum of (1) the
average of the emission factors reported for secondary production and die casting through EPA's magnesium
Partnership (excluding outliers), and (2) the standard deviation of those emission factors. The 1.6 kg-per-ton factor
is higher than most, though not all, of the emission factors reported, which ranged from 0.7 to 7 kg/ton Mg in 2006.
Thus, it is somewhat conservative, but not unreasonably so.
The numbers of facilities and quantities of emissions covered by each of the thresholds considered are presented in
Tables 1 and 2 below.
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Table 1. Threshold Analysis for Mg Production Based On Emissions
Threshold
Level
mtCO2e/yr
100,000
25,000
10,000
1,000
Total
Nationwide
Emissions
mtCO2e/Yr
3,200,000
3,200,000
3,200,000
3,200,000
Nationwide
Number of
Facilities1
13
13
13
13
Emissions Covered
mtCO2e/yr
2,872,982
2,939,741
2,939,741
2,954,559
Percent
89.8%
91 .9%
91 .9%
92.3%
Facilities Covered
Number of
Facilities
9
11
11
13
Percent
69%
85%
85%
100%
Table 2. Threshold Analysis for Mg Production Based On Mg Production Capacity
Capacity
Threshold
Level
mt Mg/yr
2,622
656
262
26
Total
Nationwide
Emissions
3,200,000
3,200,000
3,200,000
3,200,000
Nationwide
Number of
Facilities1
13
13
13
13
GHG Emissions Reported
mtCO2e/yr
2,780,717
2,949,732
2,949,732
2,954,559
Percent
86.9%
92.2%
92.2%
92.3%
Affected Facilities
Number of
Facilities
9
12
12
13
Percent
69%
92%
92%
100%
As can be seen from the tables, the coverages of the emissions and capacity-based thresholds are similar but not
identical, with the 25,000- and 10,000-mtCO2e thresholds covering one less facility than the 656- and 262-metric-
ton-of-magnesium thresholds. The emissions threshold of 25,000 mtCO2e is estimated to cover all currently
operating U.S. primary and secondary magnesium producers and most die casters, accounting for over 99 percent of
emissions from these source categories.
A key advantage of the emission-based thresholds is that they take into account the variability in cover gas
identities, usage rates, and process conditions. In facilities where SF6 is used, the usage rate can vary by an order of
magnitude depending on the casting process and operating conditions. Alternatives to SF6 have considerably lower
GWPs than SF6, adding to the potential variability. Because emissions of each cover gas are assumed to equal use,
and facilities are expected to track use in the ordinary course of business, facilities would have little difficulty
determining whether or not they must report under an emission-based threshold.
Table 3 below presents the amounts of cover gas species that equal a reporting threshold of 25,000 mtCO2e.
Table 3. Threshold Translation to Weight of Gas using 100-year GWP*
25,000 mtCO2e.
is equal to:
1,046 kg SF6
19,231 kg HFC-134a
25,000,000 kg CO2 or FK 5-1-12
To determine whether or not they exceeded an emission threshold of 25,000 mtCO2e, magnesium production and
processing facilities would multiply the total consumption of each cover or carrier gas by a GWP and unit
conversion factor. Facilities would calculate the CO2 equivalent of their cover gas usage based on the following
expression:
ESF& + E134a + EPK + ECO2 + EOG > 25,000 metric tons ofCO2 Eq.
ESF6=CSF6x23.9
El34a= C]S4a x 1.3
EFK=CFKx 0.001
Ec02=Cc02x 0.001
EOG = COG* GWPOG/1000
1 This estimate includes all primary and secondary production facilities and most die casting facilities. It excludes a
few die casting facilities as well as facilities that perform other types of casting, such as wrought and anode casting.
These types of casting generally occur at much lower volumes than die casting.
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where,
ESF6 is emissions of SF6 from magnesium production and processing (mtCO2e.)
E134a is emissions of HFC-134a from magnesium production and processing (mtCO2e)
EFK is emissions of FK 5-1-12 from magnesium production and processing (mtCO2e)
ECo2 is emissions of CO2 from magnesium production and processing (mtCO2e)
EQG is emissions of other fluorinated GHGs from magnesium production and processing (mtCO2e.)
CSF6 is annual consumption of SF6 based on facility tracking (kg)
Ci34ais annual consumption of HFC-13 4a based on facility tracking (kg)
Cpicis annual consumption of FK 5-1-12 based on facility tracking (kg)
CCo2 is annual consumption of CO2 based on facility tracking (kg)
COG is annual consumption of other fluorinated GHGs based on facility tracking (kg)
GWPOGis the Global Warming Potential of other fluorinated GHGs
The values 23.9, 1.3, and 0.001 are simple factors for converting kg of gas to mtCO2e.
Consumption of cover gases or carrier gases is estimated by monitoring changes in container masses and inventories
using a number of different possible methods, as described in Section 3 below
3. Options for Monitoring Methods
EPA reviewed a range of protocols and guidance for this analysis. These protocols included the 2006IPCC
Guidelines, EPA's SF6 Emission Reduction Partnership for the Magnesium Industry, the Inventory of U.S.
Greenhouse Gas Emissions and Sinks, the Technical Guidelines for the Voluntary Reporting of Greenhouse Gases
(1605(b)) Program, EPA's Climate Leaders Program, and The Climate Registry.
The methods described in these protocols and guidance coalesce around the methods described by the IPCC
guidelines and U.S. Inventory methodology. These methods range from a lower tiered (Tier 1) approach based on
magnesium metal processed to a higher-tiered (Tier 3) approach based on facility-specific analytic monitoring data.
a. Option 1: Default Emission Eactor
Option 1, which is the same as the IPCC Tier 1 approach, equates cover gas emissions to the product of a default
emission factor and the quantity of magnesium produced or processed. Though this method is simple, the default
emission factor for the SF6 usage and emissions rate is significantly uncertain due to the variability in production
processes and operating conditions. As discussed above, the SF6 usage rate can vary by an order of magnitude in
facilities where SF6 is used, depending on the casting process and operating conditions. Moreover, alternatives to
SF6 have considerably lower GWPs than SF6, adding to the potential variability.
b. Option 2: Cover Gas Consumption
Option 2 for monitoring emissions of GHG cover gases is similar to the Tier 2 approach in the 2006 IPCC
Guidelines for magnesium production. This approach is based on facility-specific SF6 tracking information for
cover gas consumption. This methodology translates to any cover gas that is a GHG, including CO2, HFC-134a and
FK 5-1-12. It does not account for any destruction of the cover or carrier gas during use.
EPA has analyzed three methods for tracking consumption of cover and carrier gases, as follows:
In the first method, consumption of cover gases or carrier gases is estimated by monitoring changes in container
masses and inventories using Equation 1 below:
Equation 1) C=IB-IE+A-D
where:
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C = Consumption of that cover gas or carrier gas in kg over the period (e.g., 1 year)
IB = Inventory of that cover gas or carrier gas stored in cylinders or other containers at the beginning
of the period (e.g., 1 year) including heels in kg.
IE = Inventory of that cover gas or carrier gas stored in cylinders or other containers at the end of the
period (e.g., 1 year) including heels in kg.
A = Acquisitions of that cover gas or carrier gas during the period (e.g., year) through purchases or
other transactions, including heels in cylinders or other containers returned to the magnesium
production or processing facility, in kg.
D = Disbursements of cover gas or carrier gas through sales or other transactions during the period,
including heels in cylinders or other containers returned by the magnesium production or processing
facility to the gas distributor, in kg.
In the second method, consumption of cover gases or carrier gases is estimated by monitoring changes in the masses
of individual containers as their contents are used, using Equation 2:
n
Equation 2) r - V O
M ' ^GHG ~ 2-t^P
P=l
where:
CGHG = The consumption of the cover gas over the period (kg)
Qp = The mass of the cover gas used over the period (kg)
N = The number of periods in the year
For purposes of Equation 2, the mass of the cover gas used over the period p is estimated by using Equation 3
below:
Equation 3) Qp = MB - ME
where:
Qp = The mass of the cover gas used over the period (kg)
MB = The mass of the contents of the cylinder at the beginning of period p
ME = The mass of the contents of the cylinder at the end of period p
In the third method, consumption of cover gases or carrier gases is estimated by using flowmeters in cover gas
distribution systems.
Any of these three methods should yield an accurate and precise estimate of cover gas usage and emissions as long
as accurate and precise weigh scales and/or flowmeters are used. Thus, a facility's choice of method will probably
depend primarily on the current equipment and methods used by that facility.
The cover gas usage rate shall be calculated using Equation 4 below:
Equation 4) RGHG = CGHG/Mg
where:
RGHG = The usage rate for a particular cover gas over the period
CGHG = The consumption of that cover gas over the period (kg)
Mg = The magnesium produced or fed into the casting process over the period (metric tons)
c. Option 3: Facility-specific measurements of emissions
The Tier 3 methodology of conducting facility-specific measurements of emissions to account for potential cover
gas destruction and byproduct formation is the most accurate, but also poses significant operational and economic
challenges for implementation because of the cost of direct emission measurements.
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4. Procedures for Estimating Missing Data
In general, it is unlikely that cover gas consumption data will be missing. Facilities are expected to know the
quantities of cover gas that they consume because facility operations rely on accurate monitoring and tracking of
costs. Facilities will possess invoices from gas suppliers during a given year and many facilities track the weight of
SF6 consumed by weighing individual cylinders prior to replacement.
However, where cover gas consumption information is missing, facilities could estimate emissions by multiplying
production by the average cover gas usage rate (kg gas per ton of magnesium produced or processed) from the most
recent period when operating conditions were similar to those for the period for which the data are missing, i.e.,
using the same cover gas concentrations and flow rates and, if applicable, casting parts of a similar size.
5. QA/QC Requirements
Options for QA/QC of reporting under the Option 2 monitoring method include the following:
• Calculation of the facility usage rate, comparison with known default values and historical data for the
facility, and investigation of any anomalies;
• Ensure that all cylinders returned to the gas supplier are weighed on a scale that is certified to be accurate
and precise to within 1%. Facilities would be required either to weigh residual gas (the amount of gas
remaining in returned cylinders) themselves or to have the gas supplier weigh it. Gas suppliers can provide
detailed monthly spreadsheet with exact residual gas amounts returned.
• All flowmeters, scales, and load cells used to measure quantities shall be calibrated using suitable NIST-
traceable standards and suitable methods published by a consensus standards organization (e.g., ASTM,
ASME, ASHRAE, or others). Alternatively, calibration procedures specified by the flowmeter, scale, or
load cell manufacturer may be used. Calibration shall be performed prior to the first reporting year. After
the initial calibration, recalibration shall be performed at least annually or at the minimum frequency
specified by the manufacturer, whichever is more frequent.
• Track cylinders leaving and entering storage with check-out sheets and weigh-in procedures before the
cylinders are put back into storage.
• Maintain invoices of cover gas purchases, check-out and weigh-in sheets, and scale calibrations.
• Ensure all production lines have provided information to the manager compiling the emissions report (if it
is not already handled through an electronic inventory system).
These measures would be useful to verify that the GHG emissions monitoring and calculations were done correctly
and accurately.
6. Reporting Procedures
Data that would be important for understanding and verifying emissions estimates would include total facility GHG
emissions and emissions by process type (primary production, secondary production, die casting, or other type of
casting). For total facility and process emissions, emissions could be reported in metric tons of SF6, HFC-134a, FK
5-1-12, CO2 (used as a carrier gas), and other fluorinated GHGs, and in mtCO2e.
Data that would be useful for understanding and verifying emissions estimates would also include the following
supplemental data (as well as the supplemental data required in the combustion and calcination sections):
• Total GHG emissions by facility and by gas in kg
• Type of production processes (e.g., primary, secondary, die casting);
• Magnesium production amount in metric tons for each process;
• Cover gas flow rate and composition;
• Amount of CO2 used as a carrier gas during reporting period;
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• If data were missing, the length of time the data were missing, the method used to estimate
emissions in their absence, and the quantity of emissions thereby estimated.
• Explanation for any significant deviation in emission rate (e.g., leak discovered in the cover gas
delivery system resulted in increased consumption); and
• Data from the prior year for comparison.
• A description of any new melt protection technologies to account for reduced emissions in a given
year.
The following records would be important for verifying and documenting emissions estimates:
(1) Records documenting the facility's adherence to the QA/QC requirements outlined above and (2)
records verifying the quantities reported above. These records include check-out and weigh-in sheets and
procedures for cylinders, residual gas amounts in cylinders sent back to suppliers, and invoices for gas
purchases or sales.
These non-emissions data are needed to understand the nature of the facilities and processes for which data
are being reported and for verifying the reasonableness of the reported data.
7. References
EPA (2008) Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2006. U.S. Environmental Protection
Agency, Washington, D.C.
IPCC (2006) 2006 IPCC Guidelines for National Greenhouse Gas Inventories. The National Greenhouse Gas
Inventories Programme, The Intergovernmental Panel on Climate Change, H.S. Eggleston, L. Buendia, K. Miwa, T
Ngara, and K. Tanabe (eds.). Hayama, Kanagawa, Japan.
USGS (2007) 2006 Minerals Yearbook - Magnesium. U.S. Geological Survey, Reston, VA.
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