Introduction
Coal mining operations, both active and abandoned, are significant sources of methane (CH4) emissions, a potent greenhouse gas (GHG). CH4 is a potent greenhouse gas with a global warming potential that is 28 times greater than carbon dioxide (CO2) over a 100-year period. Methane is found naturally in coal seams and is released during the coal mining process due to pressure changes and fractures in the coal seam.
The primary sources of coal mine methane (CMM) emissions include:
- Active Mines: CH4 is released during the mining process from coal seams and surrounding rock strata. These include underground and surface mining operations.
- Underground Mining: Methane is released during mining operations from deep underground seams.
- Surface or Open Pit Mines: Exposure of coal seams in surface mining operations allows CH4 to escape into the atmosphere.
- Abandoned Mines: Abandoned mines can continue to emit CH4 for many years.
Secondary GHG emissions from coal mines include enclosed flares, open flares and other thermal oxidation technologies used to combust methane emissions and internal combustion engines that use the coal mine methane as a fuel source.
This blog focuses on active mines where CH4 emissions can more easily be recovered and controlled.
- Pre-Drainage- Methane is extracted prior to the mining and it involves drilling for boreholes into the coal seam. Enclosed flares or open flares are often utilized as the methane concentrations are high enough to sustain combustion.
- Post-Drainage- Methane is extracted from the coal seams after the mining has commenced and it involves drilling of boreholes into the areas where the coal has been extracted. Enclosed flares or open flares are often utilized as the methane concentrations are high enough to sustain combustion
- Ventilation Systems: Underground coal mines are ventilated with fresh air utilizing large fans to reduce the CH4 concentration to less than 1% at the coal face and within the mine workings. This mixture of CH4 and ventilation air is known as Ventilation Air Methane (VAM).
Underground Coal Mine Vent Gas Characteristics
The primary component of coal mine vent gas is CH4. Other gases include carbon dioxide (CO2) and nitrogen (N2) and other hydrocarbons. When combined with ventilation air, the mixture will contain CH4, other hydrocarbons, CO2, N2 and oxygen (O2).
VAM is the main source of CH4 emissions from underground coal mines. VAM makes up approximately 70% of all coal mine methane emissions. Typical VAM (mixture of CH4 and air) flow rates range from 300,000 – 1,200,000 cubic feet per min (cfm).
U.S. Reported GHG Emissions from Underground Coal Mines
According to the USEPA’s 2022 Greenhouse Gas Reporting Program (GHGRP) data for, 61 underground coal mine facilities in 10 states across the U.S. collectively emitted 26.496 million metric tons of CO2e into the atmosphere.
GHGRP reported underground coal mine GHG emissions can be easily obtained using the USEPA’s FLIGHT (Facility Level Information on GreenHouse gases Tool). The tool lets the user select data for the “Underground Coal Mines” sector and the reporting year needed.
Note that the FLIGHT data includes GHG emissions only from 2011 onwards and solely for those underground coal mines that triggered reporting under USEPA GHG rules in 40 CFR Part 98.
USEPA Greenhouse Gas Reporting Requirements
The EPA greenhouse gas (GHG) reporting rules in 40 CFR 98 subpart FF apply to underground coal mines. Active and under development underground coal mines must report GHG emissions to the USEPA if the coal mine releases 36,500,000 actual cubic feet of CH4 or more per year.
This category excludes abandoned, closed, and surface coal mines, as well as post-mining coal activities.
At standard conditions of 60 degrees F and 1 atmosphere, 36,500,000 cubic feet of CH4 is approximately 700 metric tons. Using a CH4 global warming potential (GWP) of 28, this equals approximately 19,600 metric tons CO2e.
Subpart FF GHGs required to be reported:
- CH4 from ventilation and degasification systems
- CH4 and CO2 from systems such as ventilation air methane (VAM) oxidizers, enclosed combustion devices (ECD) or flares.
Underground mines are also required to report GHG emissions from stationary fuel combustion units (e.g., generator engines) according to 40 CFR 98 subpart C – General Stationary Fuel Combustion Sources. This includes CO2, CH4 and N2O emissions from fuel combustion.
U.S. Inventory of Greenhouse Gas Emissions and Sinks
The EPA’s 1990 – 2022 U.S. Inventory of Greenhouse Gas Emissions and Sinks (EPA-R-24-004) includes data on coal mine methane (CMM). The report supplies GHG emission estimates from underground mining, surface mining and post-mining (coal-handling) activities. This is a separate report from the FLIGHT data. For 2022, the EPA report gave the following estimated emissions from all coal mining sources:
Coal Mine Methane Emission Control
Emission controls used for coal mine methane include the following:
- Enclosed combustion devices (ECD)
- Open tip flares
- Absorption technologies
- Regenerative thermal oxidation (RTO)
Cimarron’s Solutions
Cimarron addresses coal mine methane emissions with advanced enclosed combustion devices (ECD), targeting emissions from active and abandoned mines. Here’s how we make a difference:
- Cost-Effective Models: Economical solutions to ensure easy implementation.
- Natural/Force Draft: Flexible operation in various mining environments.
- Remote Connectivity: Real-time monitoring data (temperature, flowrates and CH4%) along with data management that is required for claiming carbon credits.
- Temperature Control: Ensures optimal CH4 destruction.
- Regulatory Compliance: Meets emissions standards with high destruction and removal efficiency (DRE).
- Customizable Options: Standard and tailored solutions for specific needs.
- Proven Installations: Extensive experience across the U.S. and Appalachian Basin.
- Comprehensive Support: Full engineering and field services throughout the equipment’s lifecycle.
Summary and Conclusions
Coal mine methane (CMM) emissions pose a significant environmental challenge due to methane’s potent greenhouse gas effects. Both active and abandoned coal mines release methane, which can be efficiently captured and controlled through various methods. In active mines, methane emissions are addressed through pre-drainage, post-drainage, and ventilation systems, with Ventilation Air Methane (VAM) being the primary contributor to methane emissions.
The U.S. EPA’s Greenhouse Gas Reporting Program (GHGRP) and Inventory of Greenhouse Gas Emissions and Sinks provide essential data on methane emissions from coal mines, highlighting the scale of the issue and the regulatory requirements for reporting. The GHGRP mandates that underground coal mines report GHG emissions if they exceed specific thresholds, ensuring that high-emitting operations are closely monitored.
Effective emission controls, such as enclosed combustion devices, open flares, and regenerative thermal oxidation, are crucial in mitigating CMM emissions. Cimarron’s advanced solutions, including enclosed combustion devices, offer flexible, cost-effective, and compliant options for methane destruction, with proven installations across key mining regions in the U.S.
Conclusion
Addressing CMM emissions is critical for reducing the overall environmental impact of coal mining. With regulatory frameworks in place, such as the EPA’s GHG reporting requirements, and the availability of advanced technologies like those offered by Cimarron, there is a clear path forward to mitigate the effects of methane emissions from coal mines. Implementing these solutions not only helps in compliance but can also further reduce GHG emissions
Cimarron – Who We Are
Cimarron’s mission is to work with our clients to create a cleaner environment. The company engineers and manufactures environmental, production and process equipment for the upstream, midstream and downstream energy industries, as well as environmental control solutions for biogas, landfills, coal mine methane, and other industrial applications.
Cimarron offers our customers the know-how and environmental expertise to meet the environmental standards of today and tomorrow. As a company, we thrive every day to make a difference through innovation, customer focus, sustainability, and operational efficiency. In addition to being present in all major regions in the US, Cimarron serves more than 45 countries around the world. From key operational centers in the United States, Italy and the United Arab Emirates, Cimarron offers ongoing service and support through its own field service personnel and strategic third-party partners, creating a cleaner environment for our customers and their shareholders.
Please contact us at sales@cimarron.com to learn more about Cimarron’s combustion technologies and robust data management systems used to reduce coal mine methane.