Appendix E - Calculation Methods Appendix

Appendix E
Calculation Methods Appendix $-$ Part II.C.3.b

II.C.3.b Fuel Combustion Emissions for Facilities with On-Site Generation or Boiler Units

Some facilities use on-site fuel combustion to run power generation, cogeneration, or boiler units, and then use the resulting electricity, steam, heat, and hot water in various subprocesses. These facilities may also source additional energy from off-site, particularly for electricity. Within the facility, however, there is no difference between consuming the portion of energy sourced from on-site units and consuming the portion of energy purchased from a third party.532F[529] For this reason, the calculations assume that the proportional use of each energy type is the same across all sources $—$ e.g., that electricity from an on-site unit and electricity sourced from the grid was used in the same proportions as the facility-wide data in question 3.9 for each subprocess. The questionnaire required facilities that reported the use of on-site power generation, cogeneration, or multipurpose nonelectric boiler units to first allocate fuel use among these units and all other on-site fuel combustion in question 3.7. For these facilities, the subprocess-specific quantities of fuel use reported in question 3.8 only represented fuel that was not first combusted in the generation or boiler units, to avoid double counting. The calculations instead used data in questions 3.9 through 3.12 on subprocess-specific use of electricity, steam, heat, and hot water to allocate the emissions from the power generation, cogeneration, and boilers to subprocesses. This mapping of fuel combustion in power generation, cogeneration, boiler units, and all other fuel combustion to electricity, steam, heat, hot water, and question 3.8 fuel use to develop subprocess-specific emission estimates is shown in figure E.1, below.

Figure E.1 Mapping of facility-wide scope 1 fuel combustion emissions to subprocess-specific estimates

Figure E.1 is a process map that shows that the facility-wide emissions are disaggregated into calculations of emissions at power generation, cogeneration, and boiler units, and all other fuel combustion. The unit-specific emissions are then mapped to electricity, steam, heat, and hot water output. The emissions associated with electricity and each of the useful thermal outputs are then used with subprocess-specific questionnaire data from questions 3.8 through 3.12 to calculate the subprocess-specific estimates.

Source: Compiled by the USITC.

Note: The “Q” labels in the diagram above indicates the question number in the Commission’s facility-level questionnaire gathering this information. USITC, Greenhouse Gas (GHG) Emissions Intensities Questionnaire: Facility-Level, 2024, section 3.

Calculating the subprocess-specific emissions for other fuel combustion (from question 3.7) is similar to the subprocess-specific fuel combustion calculation for facilities with less complicated energy sourcing. The only difference is that the facility-wide emissions are multiplied by an additional ratio to remove the fuel-specific emissions associated with generation and boiler units (equation E.16). This ratio is the amount of fuel used in all other on-site fuel combustion in question 3.7 ( $u s e_{f u e l, o t h e r c o m}$ ) divided by the total fuel use reported in question 3.7 ( $Σ_{u n i t} (u s e_{f u e l, u n i t})$ ).

$\begin{matrix} S 1 F C_{f u e l, o t h e r c o m, s u b p r o c} = f a c i l i t y G H G_{f u e l} * \frac{u s e_{f u e l, o t h e r c o m}}{Σ_{u n i t} (u s e_{f u e l, u n i t})} * \frac{u s e_{f u e l, s u b p r o c}}{Σ_{s u b p r o c} (u s e_{f u e l, s u b p r o c})} (E .16) \end{matrix}$

As shown in figure E.1, fuel combustion quantities from question 3.7 ( $u s e_{f u e l, p o w e r}$ , $u s e_{f u e l, c o g e n}$ , $u s e_{f u e l, b o i l e r}$ ) determine the share of the facility-wide, fuel-specific emissions to apply to the facility’s power generation, cogeneration, and boiler units, respectively. Cogeneration units produce a mix of electricity and useful thermal outputs (steam, heat, and hot water), and boilers may produce more than one type of useful thermal output. Equations E.17 $-$ E.19 first compute the fuel combustion emissions for each of these units ( $S 1 F C_{f u e l, p o w e r}$ , $S 1 F C_{f u e l, c o g e n}$ , $S 1 F C_{f u e l, b o i l e r}$ ), before further allocating the unit emissions to their different energy outputs.

$\begin{matrix} S 1 F C_{f u e l, p o w e r} = f a c i l i t y G H G_{f u e l} * \frac{u s e_{f u e l, p o w e r}}{Σ_{u n i t} (u s e_{f u e l, u n i t})} (E .17) \end{matrix}$

$\begin{matrix} S 1 F C_{f u e l, c o g e n} = f a c i l i t y G H G_{f u e l} * \frac{u s e_{f u e l, c o g e n}}{Σ_{u n i t} (u s e_{f u e l, u n i t})} (E .18) \end{matrix}$

$\begin{matrix} S 1 F C_{f u e l, b o i l e r} = f a c i l i t y G H G_{f u e l} * \frac{u s e_{f u e l, b o i l e r}}{Σ_{u n i t} (u s e_{f u e l, u n i t})} (E .19) \end{matrix}$

The fuel-specific emissions for each unit are then totaled across fuel types to estimate total fuel combustion emissions for each unit. The formula for power generation units is shown as an example in equation E.20.

$\begin{matrix} S 1 F C_{p o w e r, e l e c} = Σ_{f u e l} (S 1 F C_{f u e l, p o w e r}) (E .20) \end{matrix}$

Before estimating subprocess-specific scope 1 emissions from electricity use, the calculations split apart emissions from cogeneration units between electricity $(S 1 F C_{c o g e n, e l e c})$ and useful thermal outputs $(S 1 F C_{c o g e n, n o n e l e c})$ . The DOE’s identification number for the facility’s cogeneration units, as reported in question 3.3c, is used to identify the unit’s electric allocation factor ( $e l e c f a c t o r_{p l a n t}$ ) in eGRID’s plant-level data.533F[530] Equation E.21 uses this factor to estimate the share of the cogeneration unit’s emissions associated with the unit’s electric power output ( $S 1 F C_{c o g e n, e l e c}$ ).

$\begin{matrix} S 1 F C_{c o g e n, e l e c} = S 1 F C_{c o g e n} * e l e c f a c t o r_{p l a n t} (E .21) \end{matrix}$

For any facilities generating more electricity than they used at the facility, the questionnaire allowed a negative value to be reported in question 4.1 for electricity purchases. Equations E.22.a and E.22.b calculate scope 1 fuel combustion emissions associated with electricity for facilities with negative net purchases and positive net purchases, respectively. Equation E.22.a incorporates the ratio of electricity used on-site, where $p u r c h_{e l e c}$ represents negative net purchases (electricity sold off-site) and ( $g e n_{p o w e r, e l e c} + g e n_{c o g e n, e l e c}$ ) is the sum of on-site electricity generation reported in question 3.3.

$I f p u r c h_{e l e c} < 0 :$

$S 1 F C_{e l e c} = \frac{(g e n_{p o w e r, e l e c} + g e n_{c o g e n, e l e c} + p u r c h_{e l e c})}{g e n_{p o w e r, e l e c} + g e n_{c o g e n, e l e c}} (S 1 F C_{c o g e n, e l e c} + S 1 F C_{p o w e r, e l e c}) (E .22. a)$

Else:

$\begin{matrix} S 1 F C_{e l e c} = S 1 F C_{c o g e n, e l e c} + S 1 F C_{p o w e r, e l e c} (E .22. b) \end{matrix}$

Then, equation E.23 allocates facility-wide scope 1 electricity generation emissions $(S 1 F C_{e l e c}$ ) to subprocesses $(S 1 F C_{e l e c, s u b p r o c})$ .

$\begin{matrix} S 1 F C_{e l e c, s u b p r o c} = S 1 F C_{e l e c} * \frac{u s e_{e l e c, s u b p r o c}}{Σ_{s u b p r o c} (u s e_{e l e c, s u b p r o c})} (E .23) \end{matrix}$

The next set of equations split emissions from non-electric cogeneration ( $S 1 F C_{c o g e n, n o n e l e c})$ and boiler units $(S 1 F C_{b o i l e r})$ to develop emissions estimates for steam, heat, and hot water use. Non-electric cogeneration emissions are the total emissions associated with on-site generation of useful thermal outputs (equations E.24 and E.25):

$\begin{matrix} S 1 F C_{c o g e n, n o n e l e c} = S 1 F C_{c o g e n} - S 1 F C_{c o g e n, e l e c} (E .24) \end{matrix}$

$\begin{matrix} S 1 F C_{c o g e n, n o n e l e c} = \sum_{u t o} S 1 F C_{c o g e n, u t o} = S 1 F C_{c o g e n, s t e a m} + S 1 F C_{c o g e n, h w a t e r} + S 1 F C_{c o g e n, h e a t} (E .25) \end{matrix}$

First, if a facility reported net sales of these outputs ( $s o l d_{u t o} > p u r c h_{u t o})$ , equations E.26.a and E.27.a applied a ratio of thermal outputs used on-site ( $g e n_{c o g e n, u t o} + g e n_{b o i l e r, u t o} - s o l d_{u t o} + p u r c h_{u t o}$ ) to outputs generated on-site ( $g e n_{c o g e n, u t o} + g e n_{b o i l e r, u t o}$ ).534F[531] This ratio removes the emissions associated with thermal outputs that were sold from the facility and used instead by third parties. When a facility sells more thermal output than it purchases, no scope 2 emissions are estimated for the quantity of purchased output; the quantity purchased is instead treated as if it were sourced from the facility’s on-site generation of that thermal output. This is consistent with how electricity was treated (using data on net electricity purchases) and with GHG Protocol guidance.535F[532] In addition to adjusting for any net sales of thermal outputs, equations E.26 and E.27 proportionally break out emissions for cogeneration and boiler units based on the relative quantities of each type of thermal output produced from each unit (e.g., ( $G E N_{c o g e n, u t o} / Σ_{u t o} (G E N_{c o g e n, u t o})$ ). Equations E.26 and E.27 are calculated for each of the types of useful thermal output (steam, heat, and hot water). Equation E.28 combines the emissions for each useful thermal output from cogeneration units with the emissions for that output from boiler units.

$I f s o l d_{u t o} > p u r c h_{u t o} :$

$\begin{matrix} S 1 F C_{c o g e n, u t o} = S 1 F C_{c o g e n, n o n e l e c} * {\frac{(g e n_{c o g e n, u t o} + g e n_{b o i l e r, u t o} - s o l d_{u t o} + p u r c h_{u t o})}{g e n_{c o g e n, u t o} + g e n_{b o i l e r, u t o}}}_{} \\ * \frac{g e n_{c o g e n, u t o}}{Σ_{u t o} (g e n_{c o g e n, u t o})} (E .26. a) \end{matrix}$

$E l s e :$

$\begin{matrix} S 1 F C_{c o g e n, u t o} = S 1 F C_{c o g e n, n o n e l e c} * \frac{g e n_{c o g e n, u t o}}{Σ_{u t o} (g e n_{c o g e n, u t o})} (E .26. b) \end{matrix}$

$I f s o l d_{u t o} > p u r c h_{u t o} :$

$\begin{matrix} S 1 F C_{b o i l e r, u t o} = S 1 F C_{b o i l e r} * {\frac{(g e n_{c o g e n, u t o} + g e n_{b o i l e r, u t o} - s o l d_{u t o} + p u r c h_{u t o})}{g e n_{c o g e n, u t o} + g e n_{b o i l e r, u t o}}}_{} \\ * \frac{g e n_{b o i l e r, u t o}}{Σ_{u t o} (g e n_{b o i l e r, u t o})} (E .27. a) \end{matrix}$

$\begin{matrix} E l s e : S 1 F C_{b o i l e r, u t o} = S 1 F C_{b o i l e r} * \frac{g e n_{b o i l e r, u t o}}{Σ_{u t o} (g e n_{b o i l e r, u t o})} (E .27. b) \end{matrix}$

$\begin{matrix} S 1 F C_{u t o} = S 1 F C_{c o g e n, u t o} + S 1 F C_{b o i l e r, u t o} (E .28) \end{matrix}$

Equation E.29 then allocates the estimates for scope 1 fuel combustion associated with the facility’s generation of steam, heat, and hot water at on-site units ( $S 1 F C_{u t o}$ ) to each of the subprocesses. The allocations for steam, heat, and hot water were reported directly in questions 3.10 $-$ 3.12 as estimated percentage shares ( $u s e s h a r e_{u t o, s u b p r o c}$ ).536F[533]

$\begin{matrix} S 1 F C_{u t o, s u b p r o c} = S 1 F C_{u t o} * u s e s h a r e_{u t o, s u b p r o c} (E .29) \end{matrix}$

Finally, equation E.30 totals the subprocess-specific estimates for scope 1 fuel combustion emissions $(S 1 F C_{s u b p r o c}$ ) from scope 1 electricity, steam, heat, hot water, and other fuel combustion. For fuel combustion not used in power generation, cogeneration, or boiler units, the subprocess-specific emissions are first totaled across all fuel types ( $Σ_{f u e l} (S 1 F C_{f u e l, o t h e r c o m, s u b p r o c})$ ).

$\begin{matrix} S 1 F C_{s u b p r o c} = Σ_{f u e l} (S 1 F C_{f u e l, o t h e r c o m, s u b p r o c}) + S 1 F C_{e l e c, s u b p r o c} + S 1 F C_{s t e a m, s u b p r o c} \\ + S 1 F C_{h e a t, s u b p r o c} + S 1 F C_{h w a t e r, s u b p r o c} (E .30) \end{matrix}$

From this point in the calculations, the allocation of any emissions from ambient heating and the aggregation of subprocesses to unit process emissions for scope 1 fuel combustion follow the same steps as with simpler facilities (equations E.11 $-$ E.13). These final steps yield scope 1 fuel combustion unit process emissions ( $S 1 F C U G H G_{p r o d u c t})$ for the product-level emissions inventories.

[529] Subject matter expert, interview by USITC staff, August 24, 2023.

[530] Variables ORISPL and ELCALLOC. EPA, “PLNT22,” January 30, 2024.

[531] Question 3.3 collected data on the quantities of thermal outputs generated from cogeneration and boiler units. Questions 3.4c-e and 3.3b collected data on sales and purchases of thermal outputs, respectively.

[532] WRI, GHG Protocol Scope 2 Guidance, 2015, 41. For a comparison of the GHG Protocol guidance and other methods, see “Other Standards Informing the Commission’s Methodology Development.”

[533] Use of steam, heat, and hot water is less common at U.S. facilities making covered steel and aluminum products than use of fuel combustion and electricity. While subprocess-specific data for fuel combustion and electricity was collected in absolute quantities to support data validation work, useful thermal output data collection was simplified to percentages to reduce burden and manage the complexity of the questionnaire’s programming.