Estimating carbon dioxide emissions from coal mines

This article is part of the Global Coal Mine Tracker, a project of Global Energy Monitor.

Download full dataset

Report an error

Sub-articles:

Global coal mines Coal mines in China Coal mines in India Coal mines in the United States Coal mines in Australia Coal mines in Russia Coal mines in Indonesia

Related-articles:

Largest coal mines in the world Coal mine impacts from Covid-19 Environmental issues of coal Coal mining Coal reserves Coal terminals

Global Energy Monitor's Global Coal Mine Tracker uses four factors to estimate the extraction based (CO₂) emissions from coal mining:

• Production
• Coal type conversion factor
• Effective CO₂ emissions factor
• Exclusion factor

Formula

The CO₂ emissions for a coal mine can be calculated with the following formula:

Annual CO₂ (in million tonnes) = Yearly production * (1- Yearly exclusion factor)* Coal type conversion factor * Effective CO₂ emissions factor

Example for a typical, non-coking bituminous coal mine:

• Production: 5 Million tonnes per annum
• Coal type conversion factor: 25.8 TJ/kt
• Effective CO₂ emissions factor: 94600 CO₂/TJ
• Conversion factor: 10^6 (tonne of CO₂/tonne of coal)
• Exclusion factor: 0.017

Based on these parameters, the annual CO₂ for the mine is as follows:
5,000,000 * (1- 0.017)* (25.8 * 94600) / 10^6 = 11,997,515 tCO₂

Coal type conversion factor

Coal type conversion factor is a measure of the energy contents per physical unit of coal subtype, or net calorific value.

In 2006, IPCC Guidelines for National Greenhouse Gas Inventories estimated the TJ/kt content for anthracite, coking coal, other bituminous coal, sub- bituminous coal, and lignite.

Coal type	Coal type conversion factor (TJ/kt)
Anthracite	26.7
Coking	28.2
Bituminous (non coking)	25.8
Sub-bituminous	18.9
Lignite	11.9

These IPCC estimates rely on data from three sources: UNFCCC Annex-1 countries’ national submissions in 2004 on 2002 emissions, International Energy Agency NCV database for all fuels (2004), and the IPCC Emission Factor Database (EFDB), version-1 (2003).

Effective CO₂ emissions factor

The variables of Effective CO₂ emissions factor include:

• Carbon content (CC): carbon mass per unit energy

• Carbon oxidation factor (COF): the percentage of carbon oxidized when combustion occurs

• Molecular weight ratio of CO₂ to C: 44/12

The formula for calculating the Effective CO₂ Emissions Factor is CC* COF* 44/12

In 2006, the IPCC Guidelines for National Greenhouse Gas Inventories estimated the CO₂ emissions factor for each type of coal in Kg CO₂ /TJ.

Coal type	Effective CO2 emissions factor(kg CO2/TJ)
Anthracite	98,300
Coking	94,600
Bituminous (non-coking)	94,600
Sub-bituminous	96,100
Lignite	101,000

Carbon content

When calculating the effective CO₂ emissions, carbon content is an influential factor because other factors tend to remain constant. The effective CO₂ emissions factor is largely a reflection of the composition of coal, since carbon content varies considerably based on carbon, hydrogen, sulphur, ash, oxygen, and nitrogen.

The default carbon content of different types of coal (kg/GJ):

Coal type	Coal carbon content (kg/GJ)
Anthracite	26.8
Coking	25.8
Bituminous (non coking)	25.8
Sub-bituminous	26.2
Lignite	27.6

Carbon dioxide emission factors are not necessarily lower for higher quality coals. For example, anthracite coal, which is the highest quality coal, produces more carbon dioxide per Btu than low-quality lignite. This is because anthracite lacks hydrogen, which is a small portion of the content of lower grade coals. When burned, hydrogen is transformed into water vapor (H₂O) rather than carbon dioxide (CO₂). Therefore, nearly all the energy in anthracite comes from the combustion of carbon, resulting in higher carbon dioxide emission rates per unit of energy than when lower grade coals containing some hydrogen are burned. (Of course, on a tonnage basis, higher grade coals do produce more carbon dioxide than lower grade coals.)

Carbon oxidation factor

The IPCC uses a default carbon oxidation factor of 1, assuming a complete oxidation of the carbon contained in the fuel.

Molecular weight ratio of CO₂ to C

Taking into account the weight ratio of CO₂ to Carbon is 44/12. According to the US Energy Information Administration, "the addition of two oxygen atoms to each carbon atom forms CO2, which has an atomic weight of 44—roughly 3.6667 times the atomic weight of the carbon, which is 12. For example, subbituminous coal is, on average, 51% carbon, so the carbon in a short ton (2,000 pounds) of subbituminous coal weighs 1,020 pounds. The CO2 emissions from burning a short ton of subbituminous coal weighs approximately 3,740 pounds, or about 3.67 times the weight of the carbon in a short ton of subbituminous coal and 1.87 times the weight of a short ton of subbituminous coal.”

Conversion factor

Emission factors for CO₂ from the IPCC are in units of kg CO2/TJ on a net calorific value basis (depending on the production units). A conversion factor of 10^6 provides tonnes of CO₂ /tonne of coal.

Exclusion factor

The exclusion factor estimates the fraction of extracted coal that is not ultimately combusted (i.e. lost along the supply chain or used for non-combustion purposes) in a given year.

The Production Gap Report 2019 estimated default exclusion factors for anthracite, bituminous coal, sub-bituminous coal, and lignite to be 0.017 (or 1.7%) of coal that is lost as dust, etc., based on 2016 data of globally averaged annual values of excluded carbon fractions that account for losses.

For coking coal, the Production Gap report estimated 0.645 (64.5%) of the carbon dioxide should be "excluded", meaning these emissions will be counted in the process fuel or industrial category (e.g. metallurgic coke used in iron and steel production) rather than as power sector emissions.

The Global Coal Mine Tracker uses the 0.017 exclusion factor (1.7%) for all coal types, since emissions from coking coal should still be counted in general inventories. When GCMT data is used for a general compilation, it uses 0.017, but when the compilation is relevant to power sector only, it includes 0.645 for coking coal.

Global Coal Mine Tracker

The Global Coal Mine Tracker relies on the following guidelines for CO₂ emissions at the mine level.

Effective CO₂ emissions used by Global Coal Mine Tracker for coal mines

Coal type	Coal type conversion factor (TJ/kt)	CO2 Emission factor (kg CO2/TJ)	Conversion Factor (tonne CO2/Tonne of Coal)	Exclusion factor
Anthracite	26.7	98,300	2.625	0.017
Bituminous (Coking)	28.2	94,600	2.668	0.017
Bituminous (non coking)	25.8	94,600	2.441	0.017
Subbituminous	18.9	96,100	1.816	0.017
Lignite	11.9	101,000	1.202	0.017

Methods for extraction based emissions

While most CO₂ emissions frameworks, such as the United Nations Framework Convention on Climate Change (UNFCCC), attribute emissions from the burning of fossil fuels to the country or entity where the fuels are burned, the Production Gap Report (2019) has pushed for a complementary “extraction-based” approach to enable countries to track the “downstream” emissions that will result from the combustion extracted fuels.

The Global Coal Mine Tracker relies on a “bottom up” extraction-based approach to calculate carbon dioxide emissions. This is modified approach (using mine-level rather than national level production) put forth in the Production Gap Report.

Bottom up approach

The Production Gap Report 2019 put together a "bottom up approach" for calculating “extraction-based” emissions:

*Bottom-up: This method involves combining national fossil fuel production statistics with default or country-specific emission factors derived from the energy and carbon contents per physical unit of fuel subtype, and accounting for the fraction of produced fuel that goes toward non-combustion uses. This enables a tiered approach with increasing levels of methodological complexity and data requirements, in a way that is consistent with the IPCC Guidelines for National Greenhouse Gas Inventories (IPCC 2006).


Top down approach

The Production Gap Report 2019 also put together a "top down approach" for calculating “extraction-based” emissions:

*Top-down: National fossil fuel production statistics are combined with globally averaged emission rates per unit of coal, oil, and gas produced. This method has the advantage of aligning with territorial emissions estimates at a global level. However, it makes a simplifying assumption that the emissions factors for each primary fuel type are the same in all countries, which can lead to over- or under- estimates since the energy and carbon contents per physical unit of fuel can vary considerably between countries and between fuel subtypes (e.g. coking coal versus lignite).

The Production Gap Report further noted that “bottom-up” emissions estimates (from extraction-based estimates) exceeded "top-down" estimates by 10-24%, indicating that "excluded carbon fractions derived from the IEA’s World Energy Balances may not sufficiently account for the amount of coal used for non-combustion purposes and/or lost along the supply chain, especially for coking coal."

Other emission factors estimates

The following carbon dioxide emission factors were estimated by the U.S. Department of Energy for coals in the United States, relying on the high heat value approach to estimate pounds CO₂ per million Btu.

Coal type	CO2 emission factors by coal (lbs/MMBtu)
Anthracite	227.4
Bituminous (non coking)	205.3
Sub-bituminous	211.9
Lignite	216.3