Surface mining

Summary

This methodology represents methane (CH₄) emissions associated with the surface mining of coal. The data and calculation methodology are sourced from the IPCC, as published in Volume 2, Chapter 4 - Fugitive Emissions of their 2006 IPCC Guidelines for National Greenhouse Gas Inventories.

The methodology

Emissions model

Fugitive emissions of greenhouse gases can arise during the surficial mining of coal through several pathways:

• Mining emissions: CH₄ emissions result from the liberation of gases during the breakage of coal and surrounding strata during mining operations

• Post-mining emissions: CH₄ is additionally released from coal during processing and transportation

• Low temperature oxidation: CO₂ is produced by the oxidation of coal carbon (C) on exposure to oxygen

• Uncontrolled oxidation: CO₂ is produced during the uncontrolled burning of coal. This may occur as a consequence of the trapping of heat produced by low temperature oxidation.

This methodology calculates mining and post-mining associated CH₄ emissions based on emissions factors which describe the rate at which CH₄ is released in relation to the quantity of coal produced (in terms of mass, i.e. tonnes). By multiplying these rates (e.g. m³ per tonne) by the annual quantity of coal produced (e.g. tonne per year), an estimate of the annual methane emissions - by volume (i.e. m³ per year) - is made. This is converted to a mass quantity using the standard value for CH₄ density provided by the IPCC guidelines.

Model data

The rate at which CH₄ is released depends on the depth of the material (e.g. rock, soil) overburden. Emissions factors are provided for three overburden depth ranges (<25 m, 25-50 m, >50 m). Each depth range is represented by:

• A mining phase emissions factor (m³ per tonne)

• A post-mining phase emission factor (m³ per tonne)

• A standard value for the density of CH₄ (0.67 tonnes per m³) which enables the conversion of volumetric to mass-based emissions

• The global warming potential of CH₄ which enables the conversion of absolute CH₄ emissions into a CO₂e quantity - i.e. the quantity of CO₂ which would exert the same atmospheric warming effect

Activity data required

Greenhouse gas emissions are directly proportionate to the mass of coal produced annually, which therefore must be provided in order to calculate.

Calculation and results

Both mining and post-mining CH₄ emissions are calculated and aggregated. Two emissions quantities are ultimately provided, representing: CH₄ and CO₂e emissions.

All emissions calculated by this methodology represent those attributable to the specified annual quantity of coal production.

Related methodologies

Other IPCC methodologies which focus on mining-associated fugitive emissions scenarios are available, covering underground mining, abandoned underground mines (tier 1 and tier 2) and methane flaring.