Average methane emissions from gas transmission and storage sector 27 percent lo wer than government estimates
By Don Santa, INGAA’s president and CEO
Earlier today, the journal Environmental Science & Technology released a report finding that methane emissions from the natural gas transmission and storage sector are 27 percent lower than the federal government’s estimate, based on the average estimate from a new study led by Colorado State University.
The study, a collaborative effort between industry, academia and an environmental group, used 2,292 new on-site measurements and equipment data from 922 facilities to build a computer model to calculate overall emissions. This is the most comprehensive on-site study conducted to date for these types of facilities. The study estimated methane emissions from the sector at 1,503 gigagrams per year, compared with 2,071 Gg/year reported in the Environmental Protection Agency’s 2012 Greenhouse Gas Inventory. The CSU-led study estimate ranged from 1,220 to 1,950 Gg/yr, while the EPA GHGI estimate ranged from 1,680 to 2,690 Gg/yr.
The CSU-led study also estimates that 0.35 percent of the methane transported by the transmission and storage sector in 2012 was released into the atmosphere, significantly lower than the EPA estimate of 0.48 percent.
Interestingly, researchers found that the equipment used in the transmission and storage sector has changed significantly since the release of a 1996 study conducted by the EPA and the Gas Research Institute, which the EPA relies upon to derive the emission factors used to calculate the sector’s methane emissions. In particular, this new study reported that companies have replaced many smaller engine-driven reciprocating compressors with larger and fewer centrifugal compressors resulting in lower emissions of unburned methane exhaust gases.
This finding is important. It underscores why the EPA needs to update the emissions factors it uses to estimate its inventory to reflect more accurately how the transmission and storage sector operates today. EPA largely relies on data from a nearly 20-year-old study to calculate its greenhouse gas inventory. While EPA has appropriately updated emission factors and estimation methods in select cases for other industry sources, including wells in the exploration and production sector, it has not for transmission and storage sector sources.
As in the first study released in February by the same groups, the new study indicates that a small number of leaks account for a disproportionally large share of overall methane released into the atmosphere.
This finding indicates a need to focus methane management measures at sites and equipment with the highest emissions profile. It also is very consistent with the direction INGAA members are voluntarily taking to reduce emissions at facilities.
INGAA, at the direction of its board, recently developed industry guidelines for Directed Inspection and Maintenance programs for natural gas pipeline compressor stations. DI&M is a well-established and EPA-recognized tool for detecting and mitigating leaks in a cost-effective manner. While INGAA members use DI&M, the guidelines will improve consistency and uniformity, which should result in further emissions reductions and help focus efforts on reducing emissions from the equipment that has the highest potential for large methane leaks. INGAA also is working with research groups to create a roadmap for developing technological innovations to make DI&M even more effective.
Columbia Pipeline Group, Dominion, Dow Chemical, Enable Gas Transmission Company, Kinder Morgan, TransCanada, Williams and the Environmental Defense Fund sponsored this study. We, at INGAA, also participated.
INGAA members already have made great strides in reducing methane releases with new technology and improved pipeline integrity and maintenance programs, as the CSU-led study indicates.
The natural gas transmission industry reduced the number of leaks along the pipe by 94 percent, preventing 122 million metric tons of CO2-equivalent emissions over the past three decades. These prevented emissions are equivalent to removing nearly one million passenger vehicles from the road each year over the 30-year period.
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