Calculating GHG emissions.
§ 98.323 Calculating GHG emissions.
(a) For each ventilation shaft, vent hole, or centralized point into which CH4 from multiple shafts and/or vent holes are collected, you must calculate the quarterly CH4 liberated from the ventilation system using Equation FF-1 of this section. You must measure CH4 content, flow rate, temperature, pressure, and moisture content of the gas using the procedures outlined in § 98.324.
Where:
CH4V = Quarterly CH4 liberated from a ventilation monitoring point (metric tons CH4).
V = Volumetric flow rate for the quarter (acfm) based on sampling or a flow rate meter. If a flow rate meter is used and the meter automatically corrects to standard temperature and pressure, then use scfm and replace “520°R/T × P/1 atm” with “1”.
MCF = Moisture correction factor for the measurement period, volumetric basis.
= 1 when V and C are measured on a dry basis or if both are measured on a wet basis.
= 1-(fH2O) when V is measured on a wet basis and C is measured on a dry basis.
= 1/[1-(fH2O)] when V is measured on a dry basis and C is measured on a wet basis.
(fH2O) = Moisture content of the CH4 emitted during the measurement period, volumetric basis (cubic feet water per cubic feet emitted gas).
C = CH4 concentration of ventilation gas for the quarter (%).
n = The number of days in the quarter where active ventilation of mining operations is taking place at the monitoring point. To obtain the number of days in the quarter, divide the total number of hours in the quarter where active ventilation is taking place by 24 hours per day.
0.0423 = Density of CH4 at 520 °R (60 °F) and 1 atm (lb/scf).
520 °R = 520 degrees Rankine.
T = Temperature at which flow is measured (°R) for the quarter.
P = Absolute pressure at which flow is measured (atm) for the quarter. The annual average barometric pressure from the nearest NOAA weather service station may be used as a default.
1,440 = Conversion factor (min/day).
0.454/1,000 = Conversion factor (metric ton/lb).
(1) The quarterly periods are:
(i) January 1-March 31.
(ii) April 1-June 30.
(iii) July 1-September 30.
(iv) October 1-December 31.
(2) Values of V, C, T, P, and, if applicable, (fH2O), must be based on measurements taken at least once each quarter with no fewer than 6 weeks between measurements. If measurements are taken more frequently than once per quarter, then use the average value for all measurements taken. If continuous measurements are taken, then use the average value over the time period of continuous monitoring.
(3) If a facility has more than one monitoring point, the facility must calculate total CH4 liberated from ventilation systems (CH4VTotal) as the sum of the CH4 from all ventilation monitoring points in the mine, as follows:
Where:
CH4VTotal = Total quarterly CH4 liberated from ventilation systems (metric tons CH4).
CH4V = Quarterly CH4 liberated from each ventilation monitoring point (metric tons CH4).
m = Number of ventilation monitoring points.
(b) For each monitoring point in the degasification system (this could be at each degasification well and/or vent hole, or at more centralized points into which CH4 from multiple wells and/or vent holes are collected), you must calculate the weekly CH4 liberated from the mine using CH4 measured weekly or more frequently (including by CEMS) according to 98.234(c), CH4 content, flow rate, temperature, pressure, and moisture content, and Equation FF-3 of this section.
Where:
CH4D = Weekly CH4 liberated from the monitoring point (metric tons CH4).
Vi = Measured volumetric flow rate for the days in the week when the degasification system is in operation at that monitoring point, based on sampling or a flow rate meter (acfm). If a flow rate meter is used and the meter automatically corrects to standard temperature and pressure, then use scfm and replace “520°R/Ti × Pi/1 atm” with “1”.
MCFi = Moisture correction factor for the measurement period, volumetric basis.
= 1 when Vi and Ci are measured on a dry basis or if both are measured on a wet basis.
= 1-(fH2O)I when Vi is measured on a wet basis and Ci is measured on a dry basis.
= 1/[1-(fH2O)i] when Vi is measured on a dry basis and Ci is measured on a wet basis.
(fH2O) = Moisture content of the CH4 emitted during the measurement period, volumetric basis (cubic feet water per cubic feet emitted gas).
Ci = CH4 concentration of gas for the days in the week when the degasification system is in operation at that monitoring point (%).
n = The number of days in the week that the system is operational at that measurement point. To obtain the number of days in the week, divide the total number of hours that the system is operational by 24 hours per day.
0.0423 = Density of CH4 at 520 °R (60 °F) and 1 atm (lb/scf).
520 °R = 520 degrees Rankine.
Ti = Temperature at which flow is measured (°R).
Pi = Absolute pressure at which flow is measured (atm).
1,440 = Conversion factor (minutes/day).
0.454/1,000 = Conversion factor (metric ton/lb).
(1) Values for V, C, T, P, and, if applicable, (fH2O), must be based on measurements taken at least once each calendar week with at least 3 days between measurements. If measurements are taken more frequently than once per week, then use the average value for all measurements taken that week. If continuous measurements are taken, then use the average values over the time period of continuous monitoring when the continuous monitoring equipment is properly functioning.
(2) Quarterly total CH4 liberated from degasification systems for the mine must be determined as the sum of CH4 liberated determined at each of the monitoring points in the mine, summed over the number of weeks in the quarter, as follows:
Where:
CH4DTotal = Quarterly CH4 liberated from all degasification monitoring points (metric tons CH4).
(CH4D)i,j = Weekly CH4 liberated from a degasification monitoring point (metric tons CH4).
m = Number of monitoring points.
w = Number of weeks in the quarter during which the degasification system is operated.
(c) If gas from a degasification system or ventilation system is sold, used onsite, or otherwise destroyed (including by flaring or VAM oxidation), you must calculate the quarterly CH4 destroyed for each destruction device and each point of offsite transport to a destruction device, using Equation FF-5 of this section. You must measure CH4 content and flow rate according to the provisions in § 98.324, and calculate the methane routed to the destruction device (CH4) using either Equation FF-1 or Equation FF-4 of this section, as applicable.
Where:
CH4Destroyed = Quarterly CH4 destroyed (metric tons).
CH4 = Quarterly CH4 routed to the destruction device or offsite transfer point (metric tons).
DE = Destruction efficiency (lesser of manufacturer's specified destruction efficiency and 0.99). If the gas is transported off-site for destruction, use DE = 1.
(1) Calculate total CH4 destroyed as the sum of the methane destroyed at all destruction devices (onsite and offsite), using Equation FF-6 of this section.
Where:
CH4DestroyedTotal = Quarterly total CH4 destroyed at the mine (metric tons CH4).
CH4Destroyed = Quarterly CH4 destroyed from each destruction device or offsite transfer point.
d = Number of onsite destruction devices and points of offsite transport.
(2) [Reserved]
(d) You must calculate the quarterly measured net CH4 emissions to the atmosphere using Equation FF-7 of this section.
Where:
CH4 emitted (net)= Quarterly CH4 emissions from the mine (metric tons).
CH4VTotal = Quarterly sum of the CH4 liberated from all mine ventilation monitoring points (CH4V), calculated using Equation FF-2 of this section (metric tons).
CH4DTotal = Quarterly sum of the CH4 liberated from all mine degasification monitoring points (CH4D), calculated using Equation FF-4 of this section (metric tons).
CH4DestroyedTotal = Quarterly sum of the measured CH4 destroyed from all mine ventilation and degasification systems, calculated using Equation FF-6 of this section (metric tons).
(e) For the methane collected from degasification and/or ventilation systems that is destroyed on site and is not a fuel input for energy generation or use (those emissions are monitored and reported under Subpart C of this part), you must estimate the CO2 emissions using Equation FF-8 of this section.
Where:
CO2 = Total quarterly CO2 emissions from CH4 destruction (metric tons).
CH4Destroyedonsite = Quarterly sum of the CH4 destroyed, calculated as the sum of CH4 destroyed for each onsite, non-energy use, as calculated individually in Equation FF-5 of this section (metric tons).
44/16 = Ratio of molecular weights of CO2 to CH4.
[75 FR 39763, July 12, 2010, as amended at 76 FR 73901, Nov. 29, 2011; 78 FR 71967, Nov. 29, 2013; 81 FR 89264, Dec. 9, 2016]
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