User defined abandoned mines
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Summary
This methodology represents methane (CH4) emissions associated with abandoned, underground coal mines. 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
After closure, coal mines may continue to emit methane as a result of in situ gases migrating through natural or manmade conduits such as old portals, vent pipes, or cracks and fissures in the overlying strata. Abandoned mines may flood as a result of groundwater intrusion or surface flow, in which case emissions from completely flooded abandoned mines can be treated as negligible. Non-flooded or partially-flooded mines can continue to produce methane (CH4) emissions over a long period of time.
This methodology calculates the annual fugitive CH4 emissions from abandoned mines, and is specifically applicable to mines considered to be 'gassy' during the period in which they were active. The methodology represents the IPCC tier 2 approach.
Emissions are calculated by deriving an emissions factor which is specific to the mine under consideration. This emissions factor is based on the known annual CH4 emissions of the mine prior to abandonment together with a decay model describing the typical decrease in this rate through time. The derived emissions factor represents the annual rate of emissions from the mine after a specific period of abandonment.
Also factored in to calculations is the quantity of CH4 which is recovered during the annual period under consideration.
Model data
Fugitive CH4 emissions are at their greatest immediately subsequent to abandonment and decrease through time thereafter. The rate at which these emissions decline through time (since abandonment) depends on the type (or 'rank') of coal mined. Decay parameters are provided for three coal ranks: anthracite, bituminous, and sub-bituminous.
Also used for calculating emissions are:
- 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
Annual CH4 - under this methodology - depend on two factors (1) the annual CH4 emissions prior to abandonment; and (2) the time since abandonment. Both of these data must therefore be specified in order to calculate.
The specification of a volume of recovered methane can also be optionally provided.
Calculation and results
CH4 emissions are calculated according to the data specified, taking into account the reduction in fugitive emissions which has occurred over the period of abandonment. From the CH4 emissions calculated, any CH4 recovered during the inventory year is then subtracted.
Two emissions quantities are ultimately provided, representing: CH4 and CO2e emissions. All emissions calculated by this methodology represent those attributable to the abandoned mine for the annual period under consideration, minus any CH4 which is recovered during that time.
Related methodologies
Other IPCC methodologies which focus on mining-associated fugitive emissions scenarios are available, covering underground and surficial active mines, the tier 1 methodology for abandoned underground mines, and methane flaring.
Where recovered methane is burned for energy production, flared, or fed into a gas distribution system, the IPCC methodologies for stationary fuel combustion, methane flaring and oil and gas processing may be of interest.