Multiday Measurements of Pneumatic Controller Emissions Reveal the Frequency of Abnormal Emissions Behavior at Natural Gas Gathering Stations

Gas-driven pneumatic controllers (PCs) and actuators used in all natural gas sectors vent uncombusted natural gas to the atmosphere during operation and contribute approximately 20% of methane emissions from the natural gas supply chain. In this study, multiday measurements were utilized to better characterize PC emission rate profiles. Emissions from 72 PCs were successfully measured at 16 gathering compressor stations for an average of 76 h each between June 2017 and May 2018. These measurements are the first known multiday recordings of emissions of PCs in situ at operating natural gas facilities. These measurements revealed previously unidentified emissions behaviors. A review by an expert panel identified 30 PCs (42% of measured devices) that exhibited abnormal emissions behavior, including 25 of 40 intermittent-vent PCs, 5 of 24 low-bleed PCs, and 0 of 8 high-bleed PCs measured. Abnormally operating PCs had emissions substantially higher than the emissions of those operating normally. For intermittent-vent PCs, abnormally operating PCs showed average emission rates of 16.1 standard ft3 h–1 (scfh, whole gas) versus 2.82 scfh for normally operating PCs. Sampling simulations also indicate that measurements of ≥24 h are necessary to quantify emissions to within 20% [11–31%] of a PC's long-term average emissions. Due to potential biases in sample size and diversity and corrections for measurement errors, we recommend these data be utilized for only a qualitative understanding of PC behavior and not for developing emission factors.