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Subpart F—Aluminum Production

§98.60 Definition of the source category.

(a) A primary aluminum production facility manufactures primary aluminum using the 

Hall-Héroult manufacturing process. The primary aluminum manufacturing process comprises 

the following operations:

(1) Electrolysis in prebake and Søderberg cells.

(2) Anode baking for prebake cells.

(b) This source category does not include experimental cells or research and development 

process units.

§98.61 Reporting threshold.

You must report GHG emissions under this subpart if your facility contains an aluminum 

production process and the facility meets the requirements of either §98.2(a)(1) or (a)(2).

§98.62 GHGs to report.

You must report:

(a) Perfluoromethane (CF4), and perfluoroethane (C2F6) emissions from anode effects in 

all prebake and Søderberg electrolysis cells.

(b) CO2 emissions from anode consumption during electrolysis in all prebake and 

Søderberg electrolysis cells.

(c) CO2 emissions from on-site anode baking.

(d) You must report under subpart C of this part (General Stationary Fuel Combustion 

Sources) the emissions of CO2, N2O, and CH4 emissions from each stationary fuel combustion 

unit by following the requirements of subpart C.

§98.63 Calculating GHG emissions.
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(a) The annual value of each PFC compound (CF4, C2F6) shall be estimated from the sum 

of monthly values using Equation F-1 of this section:

Where:

EPFC = Annual emissions of each PFC compound from aluminum production (metric tons 

PFC).

Em = Emissions of the individual PFC compound from aluminum production for the 

month “m” (metric tons PFC).

(b) Use Equation F-2 of this section to estimate CF4 emissions from anode effect duration 

or Equation F-3 of this section to estimate CF4 emissions from overvoltage, and use Equation F-4 

of this section to estimate C2F6 emissions from anode effects from each prebake and Søderberg 

electrolysis cell.

Where:

ECF4 = Monthly CF4 emissions from aluminum production (metric tons CF4).

SCF4 = The slope coefficient ((kg CF4/metric ton Al)/(AE-Mins/cell-day)).

AEM = The anode effect minutes per cell-day (AE-Mins/cell-day).

MP = Metal production (metric tons Al), where AEM and MP are calculated monthly.

Where:

ECF4 = Monthly CF4 emissions from aluminum production (metric tons CF4).

EFCF4 = The overvoltage emission factor (kg CF4/metric ton Al).

MP = Metal production (metric tons Al), where MP is calculated monthly.
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Where:

EC2F6 = Monthly C2F6 emissions from aluminum production (metric tons C2F6).

ECF4 = CF4 emissions from aluminum production (kg CF4).

FC2F6/CF4 = The weight fraction of C2F6/CF4 (kg C2F6/kg CF4).

0.001 = Conversion factor from kg to metric tons, where ECF4 is calculated monthly.

(c) You must calculate and report the annual process CO2 emissions from anode 

consumption during electrolysis and anode baking of prebake cells using either the procedures in 

paragraph (d) of this section, the procedures in paragraphs (e) and (f) of this section, or the 

procedures in paragraph (g) of this section.

(d) Calculate and report under this subpart the process CO2 emissions by operating and 

maintaining CEMS according to the Tier 4 Calculation Methodology in §98.33(a)(4) and all 

associated requirements for Tier 4 in subpart C of this part (General Stationary Fuel Combustion 

Sources).

(e) Use the following procedures to calculate CO2 emissions from anode consumption 

during electrolysis:

(1) For Prebake cells: you must calculate CO2 emissions from anode consumption using 

Equation F-5 of this section:

Where:

ECO2 = Annual CO2 emissions from prebaked anode consumption (metric tons CO2).

NAC = Net annual prebaked anode consumption per metric ton Al (metric tons C/metric 

tons Al).
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MP = Annual metal production (metric tons Al).

Sa = Sulfur content in baked anode (percent weight).

Asha = Ash content in baked anode (percent weight).

44/12 = Ratio of molecular weights, CO2 to carbon.

(2) For Søderberg cells you must calculate CO2 emissions using Equation F-6 of this 

section:

Where:

ECO2 = Annual CO2 emissions from paste consumption (metric ton CO2).

PC = Annual paste consumption (metric ton/metric ton Al).

MP = Annual metal production (metric ton Al).

CSM = Annual emissions of cyclohexane soluble matter (kg/metric ton Al).

BC = Binder content of paste (percent weight).

Sp = Sulfur content of pitch (percent weight).

Ashp = Ash content of pitch (percent weight).

Hp = Hydrogen content of pitch (percent weight).

Sc = Sulfur content in calcined coke (percent weight).

Ashc = Ash content in calcined coke (percent weight).

CD = Carbon in skimmed dust from Søderberg cells (metric ton C/metric ton Al).

44/12 = Ratio of molecular weights, CO2 to carbon.

(f) Use the following procedures to calculate CO2 emissions from anode baking of 

prebake cells:
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(1) Use Equation F-7 of this section to calculate emissions from pitch volatiles 

combustion.

Where:

ECO2PV = Annual CO2 emissions from pitch volatiles combustion (metric tons CO2).

GA = Initial weight of green anodes (metric tons).

Hw = Annual hydrogen content in green anodes (metric tons).

BA = Annual baked anode production (metric tons).

WT = Annual waste tar collected (metric tons).

44/12 = Ratio of molecular weights, CO2 to carbon.

(2) Use Equation F-8 of this section to calculate emissions from bake furnace packing 

material.

Where:

ECO2PC = Annual CO2 emissions from bake furnace packing material (metric tons CO2).

PCC = Annual packing coke consumption (metric tons/metric ton baked anode).

BA = Annual baked anode production (metric tons).

Spc = Sulfur content in packing coke (percent weight).

Ashpc = Ash content in packing coke (percent weight).

44/12 = Ratio of molecular weights, CO2 to carbon.

(g) If process CO2 emissions from anode consumption during electrolysis or anode 

baking of prebake cells are vented through the same stack as any combustion unit or process 

equipment that reports CO2 emissions using a CEMS that complies with the Tier 4 Calculation 
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Methodology in subpart C of this part (General Stationary Fuel Combustion Sources), then the 

calculation methodology in paragraphs (d) and (e) of this section shall not be used to calculate 

those process emissions. The owner or operation shall report under this subpart the combined 

stack emissions according to the Tier 4 Calculation Methodology in §98.33(a)(4) and all 

associated requirements for Tier 4 in subpart C of this part (General Stationary Fuel Combustion 

Sources).

§98.64 Monitoring and QA/QC requirements.

(a) Effective December 31, 2010 for smelters with no prior measurement or effective 

December 31, 2012, for facilities with historic measurements, the smelter-specific slope 

coefficients, overvoltage emission factors, and weight fractions used in Equations F-2, F-3, and 

F-4 of this subpart must be measured in accordance with the recommendations of the EPA/IAI

Protocol for Measurement of Tetrafluoromethane (CF4) and Hexafluoroethane (C2F6) Emissions 

from Primary Aluminum Production (2008) (incorporated by reference, see §98.7), except the 

minimum frequency of measurement shall be every 10 years unless a change occurs in the 

control algorithm that affects the mix of types of anode effects or the nature of the anode effect 

termination routine.Facilities which operate at less than 0.2 anode effect minutes per cell day or 

operate with less than 1.4mV anode effect overvoltage can use either smelter-specific slope 

coefficients or the technology specific default values in Table F-1 of this subpart.

(b) The minimum frequency of the measurement and analysis is annually except as 

follows:

(1) Monthly for anode effect minutes per cell day (or anode effect overvoltage and 

current efficiency).

(2) Monthly for aluminum production.
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(3) Smelter-specific slope coefficients, overvoltage emission factors, and weight fractions 

according to paragraph (a) of this section.

(c) Sources may use either smelter-specific values from annual measurements of 

parameters needed to complete the equations in §98.63 (e.g., sulfur, ash, and hydrogen contents) 

or the default values shown in Table F-2 of this subpart.

§98.65 Procedures for estimating missing data.

A complete record of all measured parameters used in the GHG emissions calculations is 

required. Therefore, whenever a quality-assured value of a required parameter is unavailable 

(e.g., if a meter malfunctions during unit operation or if a required sample measurement is not 

taken), a substitute data value for the missing parameter shall be used in the calculations, 

according to the following requirements:

(a) Where anode or paste consumption data are missing, CO2 emissions can be estimated 

from aluminum production by using Equation F-9 of this section.

ECO2 = EFp x MPp + EFs x MPs (Eq. F-9)

Where:

ECO2 = CO2 emissions from anode and/or paste consumption, metric tons CO2.

EFp = Prebake technology specific emission factor (1.6 metric tons CO2/metric ton 

aluminum produced).

MPp = Metal production from prebake process (metric tons Al).

EFs = Søderberg technology specific emission factor (1.7 metric tons CO2/metric ton Al 

produced).

MPs = Metal production from Søderberg process (metric tons Al).
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(b) For other parameters, use the average of the two most recent data points after the 

missing data.

§ 98.66 Data reporting requirements.

In addition to the information required by § 98.3(c), you must report the following 

information at the facility level:

(a) Reserved.

(b) Type of smelter technology used.

(c) The following PFC-specific information on an annual basis:

(1) Perfluoromethane emissions and perfluoroethane emissions from anode effects in all 

prebake and all Søderberg electrolysis cells combined.

(2) Anode effect minutes per cell-day (AE-mins/cell-day), anode effect frequency

(AE/cell-day), anode effect duration (minutes). (Or anode effect overvoltage factor ((kg 

CF4/metric ton Al)/(mV/cell day)), potline overvoltage (mV/cell day), current efficiency (%).)

(3) Smelter-specific slope coefficients (or overvoltage emission factors) and the last date 

when the smelter-specific slope coefficients (or overvoltage emission factors) were measured.

(d) Method used to measure the frequency and duration of anode effects (or overvoltage).

(e) The following CO2-specific information for prebake cells:

(1) Annual anode consumption if using the method in § 98.63(g).

(2) Annual CO2 emissions from the smelter.

(f) The following CO2-specific information for Søderberg cells:

(1) Annual paste consumption if using the method in § 98.63(g).

(2) Annual CO2 emissions from the smelter.

(g) Reserved.
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(h) Exact data elements required will vary depending on smelter technology (e.g., pointfeed prebake or Søderberg) and process control technology (e.g., Pechiney or other).

§ 98.67 Records that must be retained.

In addition to the information required by § 98.3(g), you must retain the following 

records:

(a) Monthly aluminum production in metric tons.

(b) Type of smelter technology used.

(c) The following PFC-specific information on a monthly basis:

(1) Perfluoromethane and perfluoroethane emissions from anode effects in prebake and 

Søderberg electolysis cells.

(2) Anode effect minutes per cell-day (AE-mins/cell-day), anode effect frequency

(AE/cell-day), anode effect duration (minutes). (Or anode effect overvoltage factor ((kg 

CF4/metric ton Al)/(mV/cell day)), potline overvoltage (mV/cell day), current efficiency (%).))

(3) Smelter-specific slope coefficients and the last date when the smelter-specific-slope 

coefficients were measured.

(d) Method used to measure the frequency and duration of anode effects (or to measure 

anode effect overvoltage and current efficiency).

(e) The following CO2-specific information for prebake cells:

(1) Annual anode consumption.

(2) Annual CO2 emissions from the smelter.

(f) The following CO2-specific information for Søderberg cells:

(1) Annual paste consumption.

(2) Annual CO2 emissions from the smelter.
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(g) Smelter-specific inputs to the CO2 process equations (e.g., levels of sulfur and ash) 

that were used in the calculation, on an annual basis.

(h) Exact data elements required will vary depending on smelter technology (e.g., pointfeed prebake or Søderberg) and process control technology (e.g., Pechiney or other).

(i) Verification software records. You must keep a record of the file generated by the 

verification software specified in § 98.5(b) for the applicable data specified in paragraphs (i)(1) 

through (30) of this section. Retention of this file satisfies the recordkeeping requirement for the 

data in paragraphs (i)(1) through (30) of this section.

(1) Slope coefficient per potline per month (kg CF4/metric ton Al)/(AE-Mins/cell-day)) 

(Equation F-2 of § 98.63).

(2) Anode effect minutes per cell-day per potline per month (AE-Mins/cell-day) 

(Equation F-2).

(3) Anode effect frequency per potline per month (AE/cell-day) (Equation F-2 of § 

98.63).

(4) Anode effect duration per potline per month (minutes) (Equation F-2).

(5) Metal production of aluminum per potline per month (metric tons) (Equation F-2).

(6) Overvoltage emission factor per potline per month (kg CF4/metric ton Al) (Equation 

F-3).

(7) Metal production of aluminum per potline per month (metric tons) (Equation F-3).

(8) Weight fraction of C2F6/CF4 per potline per month (kg C2F6/kg CF4) (Equation F-4 of 

§ 98.63).

(9) Net annual prebaked anode consumption (metric tons C/metric tons Al) (Equation F-5

of § 98.63).
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(10) Annual metal production of aluminum (metric tons) (Equation F-5).

(11) Sulfur content in baked anode (weight percent) (Equation F-5).

(12) Ash content in baked anode (weight percent) (Equation F-5).

(13) Annual paste consumption (metric ton/metric ton Al) (Equation F-6 of § 98.63).

(14) Annual metal production of aluminum (metric tons) (Equation F-6).

(15) Annual emissions of cyclohexane soluble matter (kg/metric ton Al) (Equation F-6).

(16) Binder content of paste (weight percent) (Equation F-6).

(17) Sulfur content of pitch (weight percent) (Equation F-6).

(18) Ash content of pitch (weight percent) (Equation F-6).

(19) Hydrogen content of pitch (weight percent) (Equation F-6).

(20) Sulfur content in calcined coke (weight percent) (Equation F-6).

(21) Ash content in calcined coke (weight percent) (Equation F-6).

(22) Carbon in skimmed dust from Søderberg cells (metric ton C/metric ton Al) 

(Equation F-6).

(23) Initial weight of green anodes (metric tons) (Equation F-7 of § 98.63).

(24) Annual hydrogen content in green anodes (metric tons) (Equation F-7).

(25) Annual baked anode production (metric tons) (Equation F-7).

(26) Annual waste tar collected (metric tons) (Equation F-7).

(27) Annual packing coke consumption (metric tons/metric ton baked anode) (Equation 

F-8 of § 98.63).

(28) Annual baked anode production (metric tons) (Equation F-8).

(29) Sulfur content in packing coke (weight percent) (Equation F-8).

(30) Ash content in packing coke (weight percent) (Equation F-8).
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§98.68 Definitions.

All terms used in this subpart have the same meaning given in the Clean Air Act and 

subpart A of this part.

Table F-1 to Subpart F of Part 98—Slope and Overvoltage Coefficients for the Calculation 

of PFC Emissions From Aluminum Production

Technology

CF4 slope coefficient

[(kg CF4/metric ton 

Al)/(AE-Mins/cell-day)]

CF4 overvoltage 

coefficient

[(kg CF4/metric ton 

Al)/(mV)]

Weight fraction 

C2F6/CF4

[(kg C2F6/kg 

CF4)]

Center Worked 

Prebake (CWPB)

0.143 1.16 0.121

Side Worked Prebake 

(SWPB)

0.272 3.65 0.252

Vertical Stud 

Søderberg (VSS)

0.092 NA 0.053

Horizontal Stud 

Søderberg (HSS)

0.099 NA 0.085

Table F-2 to Subpart F of Part 98—Default Data Sources for Parameters Used for CO2

Emissions

Parameter Data source

CO2 Emissions from Prebake Cells (CWPB and SWPB)

MP: metal production (metric tons Al) Individual facility

records.

NAC: net annual prebaked anode consumption per metric ton Al (metric 

tons C/metric tons Al)

Individual facility

records.

Sa: sulfur content in baked anode (percent weight) 2.0.

Asha: ash content in baked anode (percent weight) 0.4.

CO2 Emissions From Pitch Volatiles Combustion (CWPB and SWPB)

MP: metal production (metric tons Al) Individual facility

records.

PC: annual paste consumption (metric ton/metric ton Al) Individual facility

records.
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CSM: annual emissions of cyclohexane soluble matter (kg/metric ton Al) HSS: 4.0.

VSS: 0.5.

BC: binder content of paste (percent weight) Dry Paste: 24.

Wet Paste: 27.

Sp: sulfur content of pitch (percent weight) 0.6.

Ashp: ash content of pitch (percent weight) 0.2.

Hp: hydrogen content of pitch (percent weight) 3.3.

Sc: sulfur content in calcined coke (percent weight) 1.9.

Ashc: ash content in calcined coke (percent weight) 0.2.

CD: carbon in skimmed dust from Søderberg cells (metric ton C/metric 

ton Al)

0.01.

CO2 Emissions from Pitch Volatiles Combustion (VSS and HSS)

GA: initial weight of green anodes (metric tons) Individual facility

records.

Hw: annual hydrogen content in green anodes (metric tons) 0.005 × GA.

BA: annual baked anode production (metric tons) Individual facility

records.

WT: annual waste tar collected (metric tons) (a) 0.005 × GA.

(a) Riedhammer furnaces (b) insignificant.

(b) all other furnaces

CO2 Emissions From Bake Furnace Packing Materials (CWPB and SWPB)

PCC: annual packing coke consumption (metric tons/metric ton baked 

anode)

0.015.

BA: annual baked anode production (metric tons) Individual facility

records.

Spc: sulfur content in packing coke (percent weight) 2.

Ashpc: ash content in packing coke (percent weight) 2.5.