Coal news and updates

A new study finds that the life-cycle of greenhouse gas emissions for electric power produced from shale gas are on par with emissions from conventional gas and on average about half those of coal.

 

The research, published in "Proceedings of National Academy of Sciences," is the most recent study to examine the GHG emissions of gas versus those of other fossil fuels and contradicts some of that earlier research.

 

The study examines and "harmonizes" the existing literature on the subject of GHG emissions from natural gas to create an "apples to apple" comparison, Garvin Heath senior scientist with the National Renewable Energy Laboratory in Golden, Colorado, and lead author of the study, said in an interview Wednesday.

 

"The systematic and robust conclusion, based on the previously published literature and our analysis is that shale gas when used to generate electricity has comparable life-cycle greenhouse gas emissions to conventionally produced natural gas," Heath said.

 

The researchers found that on the basis of grams of CO2 equivalent per kilowatt hour, the median level of emissions from shale gas were 460 g CO2e/kWh, about equal to that of conventional natural gas and less than half the median estimate of 980 g CO2e/kWh for coal. 

 

"The best performing coal facilities could have small overlap" with the life-cycle emissions of the least efficient gas-fired facilities, Heath said. 

 

In addition, the study found that assumptions about the lifetime production of wells and the practice of liquids unloading to have the greatest influence on how the estimated life-cycle GHG emissions are calculated.

 

ACTUAL MEASUREMENTS

 

In the study, Heath and co-authors -- Patrick O'Donoughue of NREL and Douglas Arent and Morgan Bazilian of the Joint Institute for Strategic Energy Analysis -- emphasized that it is important that future research should include taking actual measurements of GHG emissions from various power-generating fuel sources, rather than relying on estimates. 

 

"Harmonization of prior estimates of GHG emissions provides greater precision, but does not fully address the questions of accuracy of our knowledge of GHG emission sources in the natural gas supply chain," Arent said in a statement. 

 

"Verified measurements of emissions from components and activities throughout the natural gas supply chain, and robust analysis of lifetime well production and the prevalence of practices to reduce emissions can help create a more robust understanding of our energy options," he said.

 

Robert Howarth, a Cornell University researcher whose earlier published findings conclude that the life-cycle GHG emissions for natural gas are greater than those of coal, disputed the conclusions of the NREL/JISEA study.

 

"I disagree, and disagree strongly, with the conclusion of the Heath et al. paper. Using the best available and most up-to-date science, I think the conclusion is inescapable that natural gas has a larger greenhouse gas footprint than do other fossil fuels," Howarth said in an email statement Wednesday.

 

Howarth argued that the authors of the more recent report relied for the most part on studies performed in 2011 and the first part of 2012 and ignored more recent studies that showed higher levels of emissions of methane, a potent greenhouse gas, from natural gas operations.

 

"Bottom line? There is a lot more methane being emitted than Heath et al. assume," he said.

 

METHANE LEAKAGE

 

In addition, Howarth said the research the NREL/JISEA team looked at measured methane and carbon dioxide emissions on a 100-year time scale. 

 

"This hugely underestimates methane's importance at shorter time scales," he said. "I believe it is quite simply wrong to focus just on the 100-year time scale, as do a growing number of other earth study scientists." 

 

Heath said that the NREL/JISEA researchers included Howarth's research results in their harmonization of the existing scientific literature. 

 

"His estimates were at the high end of the other ones in the literature," he said. "Harmonization is not meant to make every estimate the same. There are legitimate differences in opinion and data resources and also the focus of different studies can differ."

 

He called the issue of methane leakage from the natural gas supply chain "an open scientific question," and one that not all of the studies in the literature addressed. "We ensured that all studies included the same set of activities," Heath said. 

 

Shawn Bennett, a spokesman for pro-energy industry group Energy In Depth, endorsed the results of the NREL/JISEA study. "What this study does is emphasize we are seeing a definite environmental benefit from the burning of natural gas," he said.

 

 

Source: Platts