Study looks at gas transmission, storage sites’ methane releases

A comprehensive study of US natural gas transmission and storage operations found total methane emissions from 2,292 on-site measurements, additional emissions data from 677 facilities, and activity data from 922 facilities were 27% lower than emissions for the industry in the US Environmental Protection Agency’s 2012 Greenhouse Gas Inventory.

The results, however, were statistically similar because of several significant, but offsetting, factors, the new report said. Movement from engines toward lower-emitting turbine and electric compressor drives and less use of gas-driven pneumatic helped reduce the study’s totals, while updated emissions rates in certain categories and explicit treatment of skewed component and facility emissions increased the numbers.

The result was an estimated gas transmission and storage methane emissions total of 1,503 gigagrams (Gg)/year, compared to EPA’s 2,071 Gg/year estimate. The study also used downwind measurements, with nitrous oxide and acetylene as tracer gases, in addition to on-site measurements of detected leaks for the first time, noted a Colorado State University (CSU) at Fort Collins researcher who led the effort.

“It’s fairly expensive to do paired measurements. Our seven gas industry partners’ support helped make that happen,” Daniel J. Zimmerle, a senior research associate at CSU’s Energy Institute, said in a July 21 teleconference. “They also provided us with data from facilities which they don’t need to report, letting us measure about 922 more locations.

“We wanted to examine if there’s a way to confirm the efficacy of on-site measures,” Zimmerle said. “We designed the protocol to specifically look at that with two methods that are scientifically independent.”

Role of ‘super-emitters’

The study also confirmed earlier findings that a relatively small number of so-called “super-emitters” contribute a large portion of releases to the total. “Finding a super-emitter is one thing. Making sure it is fixed is another,” said a second teleconference participant, Jonathan Peress, natural gas air policy director at the Environmental Defense Fund, which also was involved in the study. “There currently is no requirement for this. We believe some sort of regime for this will be necessary.”

Based on the study’s results, an estimated one in 25 storage and transmission facilities may be emitting 300 scf/min or more of gas at any given time. These releases account for about one third of fugitive emissions, and a quarter of all methane emissions from the sector annually, it indicated.

A third teleconference participant, Tom Hutchins, vice-president for environmental health and safety in Kinder Morgan Inc.’s (KMI) gas business, said that he hoped EPA would use some of the study’s data to improve its greenhouse gas inventory. “It has been scaling up numbers from the early ‘90s, and there’s been a lot of growth since—principally in turbine installations, and especially in the transmission industry,” he told reporters.

Interstate gas pipelines already have a directed inspection and maintenance (DIM) program under way to find and fix super-emitters’ leaks, Hutchins said. “Policymakers should find ways to help industry do this,” he suggested. We believe we can do better as an industry, and hope DIM will help us reach this goal.”

Researchers from Carnegie Mellon University in Pittsburgh and Aerodyne Research also worked on the study, with support from Dominion, Dow Chemical, Enable Gas Transmission, KMI, Columbia Pipeline Group, TransCanada Corp., and Williams Cos. Inc. The Interstate Natural Gas Association of America also participated.

Contact Nick Snow at nicks@pennwell.com.

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