Methane Destruction Efficiency of Natural Gas Flares
Associated with Shale Formation Wells
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Abstract
Flaring to dispose of natural gas
has increased in the United States
and is typically assumed to be 98% efficient, accounting for both
incomplete combustion and venting during unintentional flame termination.
However, no in situ measurements of flare emissions have been reported.
We used an aircraft platform to sample 10 flares in North Dakota and
1 flare in Pennsylvania, measuring CO<sub>2</sub>, CH<sub>4</sub>,
and meteorological data. Destruction removal efficiency (DRE) was
calculated by assuming a flare natural gas input composition of 60–100%
CH<sub>4</sub>. In all cases flares were >99.80 efficient at the
25%
quartile. Crosswinds up to 15 m/s were observed, but did not significantly
adversely affect efficiency. During analysis unidentified peaks of
CH<sub>4</sub>, most likely from unknown venting practices, appeared
much larger in magnitude than emissions from flaring practices. Our
analysis suggests 98% efficiency for nonsputtering flares is a conservative
estimate for incomplete combustion and that the unidentified venting
is a greater contributor to CH<sub>4</sub> emissions