IPCC methodology for surface mining fugitive emissions

Contents

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.

Only the first two sources of emissions are considered in this methodology: low temperature oxidation is typically insignificant (especially where rehabilitation practices are employed); uncontrolled oxidation is sometimes significant but extremely difficult to quantify.

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)

The methodology also uses two additional values for making the final emissions calculations

  • 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.


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