§ 98.63
Calculating GHG emissions.
(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:

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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.

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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.
$ER30OC09.027$
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:

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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).
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:

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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:

(1) Use Equation F-7 of this section to calculate emissions from pitch volatiles combustion.

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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.

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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 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).

[74 FR 56374, Oct. 30, 2009, as amended at 75 FR 79155, Dec. 17, 2010]