US DOE funds study on methane emissions from natural gas compressor stations

Natural gas, a clean-burning fuel, is gaining traction in the US as a “bridge fuel” in the path to the future of sustainable energy. However, its climate benefits are highly dependent upon the emission rate of methane from the vast natural gas infrastructure in the country.

Colorado State University, home to some of the world’s top researchers on methane emissions, will lead a two-year, US$1.8 million US Department of Energy (DOE)-funded project to analyze emissions from a specific part of the natural gas supply chain: compressor stations.

The new project, led by Daniel Zimmerle, senior researcher at CSU’s Energy Institute, will help scientists develop a more complete picture of overall emissions.CSU, engineering firm AECOM and industry partners will conduct a 20- to 26-week field campaign focusing on natural gas gathering compressor stations.

The CSU team includes co-principal investigator Anthony Marchese, professor of mechanical engineering, who previously led an Environmental Defense Fund study to measure methane emissions from gathering and processing facilities.

Methane is the primary component of natural gas and a powerful greenhouse gas with a global warming potential 84 times that of carbon dioxide over a 20-year time frame.

Although atmospheric methane originates from many sources, the natural gas sector has received the most scrutiny for emissions. Significant quantities of methane are emitted from its million-plus miles of pipeline, half million wells, and thousands of gathering, processing, transmission, storage and distribution facilities.

Natural gas from wells is “gathered” into pipelines and boosted in pressure at compressor stations for transport to downstream processing plants and on to the transmission system. The CSU study is expected to measure emissions from 80 compressor stations nationwide and more than 300 individual compressor units.

Marchese’s prior study (co-authored by Zimmerle) looked at 114 gathering compressor stations and 16 processing plants in 13 US states. Twenty percent of those facilities showed methane emissions – including both leaks and non-leak sources – of more than 1%.

The study concluded that the gathering and processing sector of the natural gas system was under-represented by a factor of 8 in the US Environmental Protection Agency (EPA) Greenhouse Gas Inventory. As a direct result of the CSU work, the inventory was updated in 2016, and gathering operations now represent 27% of all methane emissions in the current inventory.

Noting that the previous study used downwind techniques to measure entire facilities at one time, Marchese said that they will get a better view of what types of emissions sources influence the facility-level emissions, component by component, in the new study.

The newly funded study is in response to a DOE-outlined need for characterizing “leak rates and leak frequencies for compressors at boosting stations, including disaggregated detail to reflect unique characteristics of different compressor types (e.g., wet seals vs. dry seals).”

The results of the study will also inform future versions of the EPA Greenhouse Gas Inventory, which now employs the CSU-derived facility-level emission rate for gathering facilities but does not yet include component-level emissions rates for these facilities.

The CSU researchers’ goal is to build a national model for methane emissions, and use that model to account for the mix of station types and activities when evaluating emissions nationally.