PROVIDING SCIENTIFIC INSIGHT INTO A CLEANER ENVIRONMENT

PROVIDING SCIENTIFIC INSIGHT INTO A CLEANER ENVIRONMENT

by Beth Lipscomb

As we make progress toward a clean energy economy, fundamental research is being conducted to ensure that cleaner fuels really do make for a cleaner environment.

To that end, the Environmental Defense Fund sponsored a comprehensive 16-part study quantifying methane leakage from the natural gas supply chain as a whole. The goal, in part, is to determine whether increased use of natural gas ultimately reduces greenhouse gases in the environment.

Colorado State University has been a key participant in this research, working with EDF and natural gas producers to determine exactly how much of the greenhouse gas methane is lost into the atmosphere from various segments of the supply chain.

THE STUDIES

The EDF study is intended to provide an estimate of the combined methane emissions from all stages of natural gas production — starting with the point at which it’s extracted and ending at the point of use.

The Energy Institute at CSU led two portions of the research: one to quantify emissions from gathering and processing; and another to examine the transportation and storage of this highly valued natural resource.

GATHERING AND PROCESSING

“The EDF reached out to CSU for this portion of the work because we have a history of working well with companies in the industry,” says Anthony Marchese, professor in the Department of Mechanical Engineering and principal investigator on the gathering and processing study. “We’re familiar with the companies as well as the equipment they use out in the field.”

Marchese also serves as director of the Engines and Energy Conversion Laboratory in the Energy Institute at CSU. His team included members from Carnegie Mellon University and Aerodyne Research.

The team first compiled data on the facilities themselves to determine the percentage of the total market held by their industry research partners. In this case, he says, the research covered about 20 percent of the total U.S. natural gas market.

Next, a field campaign was designed to measure methane emissions from 130 facilities over the course of 20 weeks and across 13 states.

After measurements were taken at those facilities they were compiled to extrapolate a national estimate for the total methane emissions from gathering and processing natural gas.

TRANSMISSION AND STORAGE

Dan Zimmerle, senior researcher and director of CSU’s Electric Power Systems Laboratory in the Energy Institute, served as principal investigator on the study of natural gas transmission compressor stations and underground storage facilities.

To make the results as reliable as possible, Zimmerle and his team used a blended approach to emissions measurement implementing both “top-down” and “bottom-up” systems at each facility (see page 16 for details on these two approaches).

The field campaign measured emissions from nine storage facilities and 36 transmission facilities. Additional measurements and public data sources helped the team build a statistical model of methane emissions across the U.S. for this sector of the natural gas industry.

THE RESULTS

SMALL LEAKS HAVE MAJOR IMPACT

Marchese’s team found that gathering facilities emit about 1,697 gigagrams (Gg) per year, and processing plants emit about 505 Gg per year. Combined, this means about one half of 1 percent of the methane produced domestically is lost during gathering and processing operations. And while that may not sound like much, he says, it’s a big deal — equivalent to the amount of natural gas consumed annually by 3.2 million U.S. homes — and a potential loss of $390 million in revenue to producers.

“It’s a higher percentage than anyone would like to see,” Marchese explains, “because our estimates are that total leakage from all natural gas operations should be less than about 1 percent in order to see immediate greenhouse gas benefits, at least for some uses of it. For instance, if we want to use natural gas to fuel cars and trucks.”

On the other hand, if gathering and processing operations account for a half of the target 1 percent that doesn’t leave a lot of room for fugitive emissions from the other segments of the supply chain.

Marchese says there’s a tolerance for a higher total leak rate — but it’s important to ensure it would be less than about 3 percent to achieve a net benefit for the environment.

He notes that once the EDF is able to synthesize all the results from all the studies of all the sectors of the industry, the total methane emissions will likely be around 1.5 percent to 2 percent of domestic natural gas production.

“GATHERING FACILITIES EMIT ABOUT 1,697 GIGAGRAMS PER YEAR, AND PROCESSING PLANTS EMIT ABOUT 505 GIGAGRAMS PER YEAR.”

WHY DO WE CARE ABOUT METHANE?

Marchese says no one wants to emit natural gas. “If we could have zero emissions, that’s what everyone would want,” he says — including gas companies and consumers alike. And there are a variety of reasons for that:

IT’S A GREENHOUSE GAS. According to the EDF, methane doesn’t linger in the atmosphere as long as carbon dioxide. But methane is 100 times more e ective in absorbing heat — making it more detrimental in the short term.

IT’S THE LARGEST COMPONENT OF NATURAL GAS. When methane is emitted, gas companies lose money. In Marchese’s study alone, the estimated 0.47 percent leak rate is equivalent to the amount of natural gas consumed annually by 3.2 million U.S. homes, and it represents a potential loss of $390 million in revenue to producers.

WHEN METHANE LEAKS, SO DO OTHER HYDROCARBONS. Other components of natural gas include ethane, propane, butane, and larger hydrocarbons. So people living near oil and gas activities may be exposed to these pollutants.

WHERE DO WE GO FROM HERE?

“We have a responsibility to make an immediate impact,” says Marchese, noting that more needs to be done to regulate existing facilities — because initial methane regulations pertain only to new installations.

The good news is that the U.S. is making progress. “In terms of methane,” Marchese says, “it appears that we’re actually ahead of the curve. Part of that is because a lot of the newer natural gas production — like hydraulic fracturing — was pioneered here in the U.S.”

On a global scale, the question is whether other countries will implement similar methane safeguards. And that remains to be seen.

“IF WE CAN FIND AND ELIMINATE THOSE FEW EMITTERS, WE CAN HAVE A BIG IMPACT ON TOTAL METHANE EMISSIONS.”

POTENTIAL FOR BIGGER IMPROVEMENTS

For the transmission and storage sector, Zimmerle’s team found that total emissions were statistically similar to previous EPA estimates — but that there were significant differences between the mix of equipment and some of the emissions rates, as compared to those the EPA tested to estimate national greenhouse gas inventory.

Based on their results, the study’s authors, who also included collaborators from Carnegie Mellon and Aerodyne Research, found that one in 25 transmission and storage facilities emit 300 standard cubic feet per minute or more of natural gas. These emissions account for about a third of total fugitive methane emissions. The study indicated that the emissions are intermittent and unpredictable – valuable information that could help inform changes in infrastructure and policy down the road.

Results varied based on factors such as the technology and equipment being used by different storage locations.

For example, increased use of gas-driven pneumatic controllers in the industry has helped to reduce emissions at specifc steps along the way. Yet other areas — like exhaust emissions — revealed higher rates of emission than previously estimated.

The overall takeaway, Zimmerle says, is that, “In most emissions categories, a relatively small number of emitters are responsible for a large portion of the emissions.” His team found that compressor vents, leaky isolation valves, reciprocating engine exhaust, and equipment leaks were major sources. “So this indicates that if we can find and eliminate those few emitters, we can have a big impact on total methane emissions,” he explains.

The EPA is already in discussions with Zimmerle to use these latest findings in generating new greenhouse gas estimates. “Now we understand, in a more comprehensive way,” he says, “which sources are really driving emissions at these facilities. So it should be possible to target our efforts at those.”

TOP-DOWN VS. BOTTOM-UP EMISSIONS MEASUREMENT

Dan Zimmerle’s team is now doing ongoing research to help resolve differing results from “top-down” and “bottom-up” methane emission measurements.

TOP-DOWN PRACTICES involve flying an aircraft over a specific area or using multiple tall towers dispersed across an area of interest. With towers, sensors are placed at multiple heights to provide concentrated measurements. When combined with wind speeds and other factors, the methane flux can be estimated for a large area.

BOTTOM-UP MEASUREMENTS are taken on-site at the point of source for an individual facility.

“What’s happened over the last ten years or so,” says Zimmerle, “is that there’s a consistent difference between the oversight data and the bottom-up data. The oversight tends to estimate larger emissions than the bottom-up.”

He says researchers haven’t been surprised that there are some differences. Oversight measurements are testing an aggregated sample of all emissions across the nation, while point-of- source measurements are not. But he says there is still a question as to exactly why there are substantial differences.

The key is figuring out which techniques tend to omit sources. “For instance,” he says, “is there a systematic failure to measure certain things at the point of source? Or is there a modeling problem — where measurements weren’t made at the same time? Or where long-tail, large emitters aren’t accurately represented?”

For the EDF study, Zimmerle’s team used a blended approach — both at the point of source and downwind of facilities, simultaneously. “So we have very strong evidence,” he says, “that with the right sort of measurement on site, we can capture the majority of emissions from a facility.”

WHAT’S NEXT?

MARCHESE SAYS THERE IS STILL MUCH TO BE DONE IN THE FIELD OF METHANE EMISSIONS SPECIFICALLY, AND IN OTHER AREAS AS WELL. FOR INSTANCE, WHILE THE NATURAL GAS INDUSTRY IS A MAJOR CONTRIBUTOR TO METHANE EMISSIONS, THERE ARE OTHER SOURCES THAT HAVE YET TO BE RESEARCHED COMPREHENSIVELY.

“THERE ARE A LOT OF ANTHROPOGENIC EMISSIONS THAT WE’LL NEED TO LOOK AT IN THE FUTURE. FOR INSTANCE, AGRICULTURAL OPERATIONS LIKE FEEDLOTS — WE DON’T HAVE A GOOD HANDLE ON THOSE YET,” HE SAYS. “ESTIMATES ARE THAT EMISSIONS FROM THOSE KINDS OF THINGS ARE NOT QUITE AS HIGH AS FROM OIL AND GAS, BUT THEY’RE NEXT ON THE LIST. AND THERE ARE ALSO LOCATIONS LIKE ABANDONED COAL MINES AND ABANDONED OIL AND GAS WELLS.”

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