Methane leaks from American natural gas distribution system dropping – study

 Natural gas distribution system benefits from better pipes and reporting

Methane emissions from the American natural gas distribution system are dropping, according to a new study that followed up on similar research from the 1990s.

In March, a group of researchers led by Washington State University’s Brian Lamb published a study called “Direct Measurements Show Decreasing Methane Emissions from Natural Gas Local Distribution Systems in the United States.”  It was part of 16 studies funded by the Environmental Defense Fund, a moderate environmental group.  It received a lot of news coverage, including articles in Fuel Fix and the New York Times.  

natural gas distribution system
By Zach Olson, executive editor, naturalgas102.com.

Prof. Lamb has been at WSU for more than 30 years, working with the University’s Laboratory for Atmospheric Research.  The laboratory was involved in a study by the Environmental Protection Agency and Gas Research Institute in the 1990s that looked at methane emissions.  When the Environmental Defense Fund was looking to update that 1992 EPA study, it reached out to Prof. Lamb and his team.  The update is important, because the EPA continues to publish greenhouse gas emissions data that relies on the 1992 findings.  Methane leaks appear to have gone down since that time.

The EPA “inventory approach” utilizes two basic numbers.  First, a given source of emissions is given an “emission factor.”  That emission factor is then multiplied by the “activity count.”  For example, the average methane leakage per mile of pipe is multiplied by the existing miles of pipe.  The EPA has not updated its emissions factors.  That means that right now, to reuse the example, the EPA is using the latest data on miles of pipe multiplied by 1992 data on leaks per mile.

The new WSU study relied on data from natural gas distribution system companies across the country who volunteered to participate.  These companies survey their pipelines on a regular basis for safety purposes.  They basically survey 20% of their pipes each year.  They pass over their pipelines with a “methane sniffer” to detect any methane leaks.  The companies grade each leak.  A grade one leak is dangerous and immediately fixed.  Grade two or three leaks are less dangerous and are scheduled for repair on some regular interval.

natural gas distribution system
Prof. Brian Lamb, Washington State University. Photo: WSU.

Prof. Lamb’s team took the list of leaks and randomly selected some of them for measurement.  They then measured the leaks to calculate an “equivalent leak,” which is essentially an average for a given type of leak.  The leaks measured were on both “mains,” the large pipes that run throughout a city, and “services,” which are the smaller pipes that branch out from a main to connect to customers.  The study looked at different types of pipes, including plastic, unprotected steel, protected steel, and cast iron.

Ultimately, the team combined their new data on equivalent leaks with the number of reported leaks on each type of pipe to come up with an average leak rate for each type of pipe in the natural gas distribution system.

The WSU study found that leaks are pretty much the same for a given type of pipe no matter where in the country you are.  Overall methane leaks do vary by region, however, because different regions have different mixes of pipe.  Cast iron is the oldest type of pipe and it is relatively leaky.  Companies are actively working to replace cast iron.

Unprotected steel and protected steel are far better than cast iron, but plastic is the best pipe for preventing methane leaks.

Prof. Lamb explained the different types of equipment used to measure methane leaks.  Companies checking their pipelines typically use a “methane sniffer,” which is a simple handheld device, to measure methane leaks with digital infrared technology.  This gives an instantaneous reading.  Leaks discovered with a sniffer are usually then measured with more precise measures, and the WSU study used more precise measures as well.

One example is a “hi-flow sampler.”  That uses similar measuring technology, but also includes an enclosure that covers the surface area where a leak is coming from.  Air is then drawn through the enclosure, so most all the methane is captured and run through the measuring device.

The biggest finding in the study is that leaks from metering and regulating (M&R) stations have come down dramatically.  These facilities are located throughout the natural gas distribution system to regulate gas pressures.  The methane leak reduction was so dramatic that the researchers went to nine of the stations included in the 1992 study to measure again and figure out what happened.  They found that in most cases equipment had been upgraded.

Older equipment was often designed to regularly release small amounts of methane in its operations, while newer equipment has lower or no emissions.

On pipes, the study found a drop in leaks, but it is less dramatic than the M&R stations.  The drops are attributed to better maintenance and a shift to less-leaky types of pipe.

Required reporting of emissions seems to have  driven much of the improvements, as natural gas distribution system grid operators tend to fix problems they are aware of.

Prof. Lamb answered some of the criticisms about his study.  The main criticism of the study is that it relied heavily on companies that wanted to demonstrate low emissions.  Prof. Lamb said the leak data was created by companies to meet safety reporting standards for the U.S. Department of Transportation, so it is unlikely to be skewed.

Additionally, the researchers made measurements at random locations chosen without collaborating with the companies.  Prof. Lamb said the one criticism that is fair is that the study relied on companies volunteering for the study.  It is possible only the best companies would volunteer.

“This was originally posted by Zach Olson on the Natural Gas 102 blog on 14 May, 2015.  He also runs a weekly podcast available on iTunes or Stitcher.”