Mitigating Mine Methane

Methane is released from underground coal mines when coal seams are disturbed. The gas is a safety hazard to underground miners, and mines must keep concentrations very low to minimize its explosion potential. Operators are required to remove methane through fans and ventilation systems that circulate fresh air from the surface. This dilutes the concentration of methane below explosive levels and releases what is referred to as ventilation air methane, or VAM. Mine safety air ventilation infrastructure is a large source of underground mining emissions both in the US and globally.

Abatement technologies exist today which can mitigate emissions from most of these sources, but they are not widely deployed. Our Coal Mine Methane Project initially focused on expanding the understanding and uptake of these commercially available technologies in the immediate future.

Mine Methane Timeline

Our Lab's work on broadening understanding of climate effects has facilitated the development and deployment of mine methane destruction projects across the US.

investigation

Complete feasibility studies

implementation

Support pipeline development of initial mine methane abatement projects

implementation

Establish abatement projects at new mines domestically

implementation

Establish abatement projects at new mines internationally

Currently

Ventilated Air Methane

VAM is the largest source of methane emissions at active coal mines. According to the EPA Coalbed Methane Outreach Program, nearly 60% of methane emissions at active coal mines are released through VAM systems. VAM is heavily diluted with air, and must be combusted using a special piece of equipment called an RTO.

Pre-Drainage Methane

Another source of methane emissions from active coal mines is gas pre-drainage from coal seams. "Gob wells" are drilled into coal seams prior to coal extraction, and gas is vacuumed from the cavities. Pre-drained gas represents a smaller portion of overall coal mine methane emissions than VAM. However, it is typically at a higher concentration than VAM, meaning it can be combusted using a standard flare.

Current Methane Destruction Technology

VAM and RTOs

Regenerative thermal oxidizers (RTOs) are combustion systems used predominantly by industries that generate VOCs. RTOs oxidize the low concentration (.3% to 1.5%) methane collected by VAM systems and have been described by the EPA as the “only commercially operational technology capable of using VAM as a primary fuel at methane concentrations below 1.5%.”

If methane concentrations are high enough, the system can produce excess heat that can be reused to generate energy to help power the RTO system. RTOs may also use steam turbine generators to produce electricity to deliver power to nearby cities or on-site operations, a practice most common at Chinese coal mines. Generally, RTOs are under-deployed at US coal mines.

Flares

Flares can achieve a methane destruction efficiency of greater than 99%, but typically require a minimum methane concentration of about 30% by volume to operate. Flares are much cheaper and easier to deploy than RTOs, and can reduce methane emissions cost effectively from mines where deploying RTOs or using the natural gas is not otherwise possible, such as at gob wells.

Flare in operation. CC Lab 2022.

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As both flares and RTOs mitigate methane emissions permanently and measurably, they generate high-quality carbon credits that meet the CC Lab's criteria.
Coal mine methane destruction projects are low-cost, permanent, verifiable, and additional for so long as coal mines emissions remain unregulated.

CC Lab site visit. CC Lab 2022.

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Risks & Risk Mitigation

New revenues for mines

As long as fugitive methane emissions are not regulated, coal mining companies have little incentive to mitigate their own emissions. Therefore, to develop CMM abatement projects, most project developers will enter agreements that are financially beneficial for the mines. Mining companies typically own the rights to coal mine gas, meaning that project developers must pay royalties to the mines to destroy it. These revenues however, represent a minor fraction of overall revenues and do not unduly support mining economics.

Government regulations

In the future, coal mines may not be shielded from carbon taxes or emissions regulation. If coal mines are required by law to mitigate methane, methane abatement projects can no longer be considered additional, and will lose the sale of carbon offsets as a key source of revenue. Investors in CMM abatement must reckon with the risk that their projects will not pay themselves back.

One option is for carbon registries to allow for the issuance of credits over a certain length of time following a project’s start date, as long as the project is installed before emissions are regulated. This could pose risks, however, if these credits are deemed non-additional.

Scaling beyond the US

The US Mine Safety and Health Administration (MSHA) upholds rigorous safety standards at mines, which has in a number of instances delayed or inhibited the installation of regenerative thermal oxidizers (RTOs).

A similar approval process must happen internationally, which could delay their deployment in target countries. Permitting will be substantially different from the US, and will require close collaboration with partners on the ground to navigate.