§ 98.63 - Calculating GHG emissions.

§ 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:

Where:

E_PFC = Annual emissions of each PFC compound from aluminum production (metric tons PFC).

E_m = 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:

E_CF4 = Monthly CF₄ emissions from aluminum production (metric tons CF₄).

S_CF4 = 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:

E_CF4 = Monthly CF₄ emissions from aluminum production (metric tons CF₄).

EF_CF4 = The overvoltage emission factor (kg CF₄/metric ton Al).

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

Where:

E_C2F6 = Monthly C₂F₆ emissions from aluminum production (metric tons C₂F₆).

E_CF4 = CF₄ emissions from aluminum production (kg CF₄).

F_C2F6/CF4 = The weight fraction of C₂F₆/CF₄ (kg C₂F₆/kg CF₄).

0.001 = Conversion factor from kg to metric tons, where E_CF4 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:

E_CO2 = 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).

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

Ash_a = 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:

E_CO2 = 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).

S_p = Sulfur content of pitch (percent weight).

Ash_p = Ash content of pitch (percent weight).

H_{p =} Hydrogen content of pitch (percent weight).

S_{c =} Sulfur content in calcined coke (percent weight).

Ash_{c =} 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.

Where:

E_CO2PV = Annual CO₂ emissions from pitch volatiles combustion (metric tons CO₂).

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

H_w = 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:

E_CO2PC = 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).

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

Ash_pc = 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]