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Energy and the Environment
Multi-day Measurements of Pneumatic Controller Emissions Reveal Frequency of Abnormal Emissions Behavior at Natural Gas Gathering Stations Benjamin Luck, Daniel Zimmerle, Timothy Vaughn, Terri Lauderdale, Kindal Keen, Matthew Harrison, Anthony J. Marchese, Laurie L Williams, and David Thomas Allen Environ. Sci. Technol. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.estlett.9b00158 • Publication Date (Web): 30 Apr 2019 Downloaded from http://pubs.acs.org on May 3, 2019
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Environmental Science & Technology Letters
Multi-day Measurements of Pneumatic Controller Emissions Reveal Frequency of Abnormal Emissions Behavior at Natural Gas Gathering Stations Benjamin Luck,† Daniel Zimmerle,∗,† Timothy Vaughn,† Terri Lauderdale,‡ Kindal Keen,‡ Matthew Harrison,¶ Anthony Marchese,†,§ Laurie Williams,k and 1
David Allen⊥ †Energy Institute, Colorado State University, Fort Collins, CO 80524, USA ‡AECOM, Austin, TX 78729, USA ¶SLR Consulting, New Braunfels, TX 78312, USA §Mechanical Engineering, Colorado State University, Fort Collins, CO 80524, USA kPhysics & Engineering, Fort Lewis College, Durango, CO 81301, USA ⊥Chemical Engineering, University of Texas, Austin, TX 78712, USA E-mail:
[email protected] Phone: +1 970 581 9945
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Abstract
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Gas-driven pneumatic controllers (PCs) and actuators used in all natural gas sec-
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tors vent uncombusted natural gas to the atmosphere during operation, and represent
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approximately 20% of methane emissions from the natural gas supply chain. In this
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study, multi-day measurements were utilized to better characterize PC emission rate
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Environmental Science & Technology Letters
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profiles. Emissions from 72 PCs were successfully measured at 16 gathering compres-
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sor stations for an average of 76 hours each between June 2017 to May 2018. These
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measurements are the first known multi-day recordings of emissions of PCs in situ at
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operating natural gas facilities. These measurements revealed previously unidentified
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emissions behaviors. Review by an expert panel identified 30 PCs (42% of measured
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devices) that exhibited abnormal emissions behavior, including 25 of 40 intermittent
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vent PCs, and 5 of 24 low bleed, and 0 of 8 high bleed PCs measured. Abnormally
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operating PCs had substantially higher emissions than those operating normally. For
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intermittent vent PCs, abnormally operating PCs showed average emission rates of
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16.11 scfh (whole gas) versus 2.82 scfh for normally operating PCs. Sampling simula-
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tions also indicate that measurements of 24 hours or more are necessary to quantify
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emissions to within 20% [11% to 31%] of a PC’s long term average emissions. Due to
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potential biases in sample size and diversity and corrections for measurement errors, we
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recommend these data only be utilized for qualitative understanding of PC behavior
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and not be used for developing emission factors.
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Environmental Science & Technology Letters
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Introduction
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Advances in hydraulic fracturing have led to a boom of natural gas production worldwide.
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Between 2000 and 2017, U.S. annual dry natural gas production increased by 40% to 26.9
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trillion standard ft3 (scf). 1 The combustion of natural gas produces less carbon dioxide
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(CO2 ) than the combustion of other fossil fuels, making it an attractive option for reducing
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greenhouse gas (GHG) emissions from power generation and transportation. However, since
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uncombusted methane (CH4 ) has a global warming potential 32 times greater than CO2 on
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a 100 year time scale and 86 times higher than CO2 on a 20 year time scale, 2 increasing
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supply chain throughput has increased attention on GHG contributions from accidental and
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operational releases of CH4 from natural gas infrastructure.
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Automated, pneumatically-actuated valves are used to control processes (liquid level,
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temperature, gas flow, and pressure) in all sectors of the natural gas industry. Isolation or
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emergency shutdown valves, and liquid or chemical injection pumps, may also be controlled
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and actuated pneumatically. Many of these process control systems use natural gas to power
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actuators because gathering stations have a continuous source of high pressure natural gas,
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eliminating the need for electrical power on remote sites or separate compression equipment
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to compress and dry ambient air. Each pneumatically-actuated valve has a dedicated con-
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troller that monitors a process variable and operates the valve to maintain the variable within
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desired limits. These pneumatic controllers (PCs) vent natural gas to the atmosphere during
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their normal operation. In 2016, PCs were estimated to emit 1257 Gg CH4 , approximately
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20% of all CH4 emissions from onshore natural gas operations. 3
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The U.S. Environmental Protection Agency (EPA) classifies PCs according to their vent-
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ing behavior as intermittent or continuous bleed. 3 Continuous bleed devices are further
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classified as low-bleed, which vent
