by Bob Shively, Enerdynamics President and Lead Facilitator

Greenhouse gas emissions by the electricity industry have declined significantly in recent years due mainly to natural gas generation displacing coal generation as well growth in renewables output and flat end-use load growth. But, there are concerns that with the shift to natural gas generation, we are not accurately accounting for the full emissions impact of using gas to generate electricity.

Source: Today in Energy, October 12, 2016, Energy Information Administration (EIA)

As stated on the Environmental Defense Fund (EDF) website:

“There has been much debate about the climate implications of increased natural gas usage. While it is true natural gas burns cleaner than other fossil fuels, methane leaking during the production, delivery and use of natural gas has the potential to undo much of the greenhouse gas benefits we think we’re getting when natural gas is substituted for other fuels.”

Leakage of natural gas, which is primarily methane, is of significant concern because methane is 28 times more potent as a greenhouse gas than carbon dioxide (which is gas released when methane is combusted) measured over a 100-year time span. Methane is even more potent when measured over a shorter time span. So any releases of methane during production, processing, transport or distribution of natural gas negate some of the benefits of shifting generation from coal to gas.

But, the good thing is that we are learning how to reduce methane leakage. Over the last few years, EDF worked with universities, research organizations, and natural gas companies in 16 studies to learn more about methane emissions. Let’s explore some of the conclusions…

The Natural Gas Delivery System

source: Enerdynamics

 
The EDF studies found the following key issues resulting in methane emissions:

Upstream

• When measured, overall emissions of methane often prove to be much higher than previous estimates.
• Emissions from equipment leaks and pneumatic devices are larger than previously thought.
• Techniques to reduce emissions from well completions are 99% effective at capturing 99% of the methane previously vented.
• Emissions from two sources, pneumatic controllers and liquids unloadings, are responsible for a significant portion of upstream methane emissions.
• Unpredictable events such as malfunctions and maintenance have a strong influence on emissions rates.
• Methane leakages from gathering systems are eight times larger than previous official estimates.
• Concentrations of super emitters (sources responsible for a disproportionate amount of methane) are widespread and unpredictable, but they can be easily identified through monitoring.

Midstream

• Compressors and equipment leaks are two primary sources of methane emissions in the midstream sector.

Downstream

• Methane emissions from local natural gas distribution systems are significant especially in regions with older infrastructure.
• Methane emissions often occur due to leaky pipelines that are not addressed because the level of leakage does not create a safety risk.
• Natural gas emissions from gas meters and from customer-owned appliances such as furnaces, boilers, and hot water heaters are significant.

EDF then identified different techniques that, coupled with better and more frequent monitoring, can reduce methane emissions. In some cases the techniques have a net savings due to value of the captured methane. In other cases, costs are high.

   Source: EDF website

The advantage is now that it is more clear what causes methane emissions, the gas industry has the knowledge to become part of the solution in increasing environmental benefits of switching from other fossil fuels to natural gas.