Coal Mine Waste Gas (Captured for Combustion)

Gassy coal mines face a choice with the methane-laden air and drainage gas their workings produce: vent it at a global warming potential of 28, or capture and combust it. The combustion route reports at 56.8 kg CO₂-e per gigajoule — the highest factor among Australia’s methane-family fuels, yet still a fraction of the venting alternative — and lands in the operator’s Scope 1 inventory.

This entry sets out the NGA Factors 2025 numbers, why this factor runs above seam gas, and three worked examples for engines, flares and capture plants.

Quick Verdict

Coal mine waste gas captured for combustion carries a combined Scope 1 emission factor of 56.8 kg CO₂-e per gigajoule under the NGA Factors 2025 (Table 5): CO₂ 51.9, CH₄ 4.6 and N₂O 0.3, at an energy content of 0.0377 GJ/m³. The unusually large methane component reflects the low, variable quality of gas drawn from mine workings. The factor applies to mine operators and waste-gas power generators combusting the gas in engines, flares or boilers, reported under Scope 1. Although it exceeds natural gas (51.53) and coal seam methane (51.63), combustion remains vastly preferable to venting, where methane reports at a GWP of 28 in CO₂-equivalent terms.

How to Calculate Coal Mine Waste Gas Emissions

Emissions (kg CO₂-e) = Energy consumed (GJ) × 56.8 kg CO₂-e/GJ

Convert cubic metres at 0.0377 GJ/m³ and megajoules at 1,000 MJ per GJ.

Worked Example 1: Waste-gas power station

A power station running on captured mine gas combusts 8,000 GJ over the year.

8,000 GJ × 56.8 = 454,400 kg CO₂-e

454.40 tonnes CO₂-e (Scope 1)

Worked Example 2: Flare and site engines

A mine’s flare and ancillary engines consume 1,500 GJ of waste gas.

1,500 GJ × 56.8 = 85,200 kg CO₂-e

85.20 tonnes CO₂-e (Scope 1)

Worked Example 3: Capture plant metered in cubic metres

A gas capture plant delivers 500,000 m³ of waste gas to combustion.

500,000 m³ × 0.0377 GJ/m³ = 18,850 GJ

18,850 GJ × 56.8 = 1,070,680 kg CO₂-e

1,070.68 tonnes CO₂-e (Scope 1)

How coal mine waste gas compares with other gaseous fuels

NGER and AASB S2 Reporting

Combustion of captured waste gas is reported as Scope 1 under the NGER scheme, separately from the fugitive methane source category that covers uncaptured mine emissions. Both totals feed the Scope 1 inventory disclosed under AASB S2, where keeping combustion and fugitives itemised makes the abatement value of your capture programme auditable.