The objective of this project is to develop: (1) nationally-representative, activity-weighted, methane emission factors for each type of equipment located at typical gathering compressor stations, suitable for use in the Environmental Protection Agency (EPA)'s Greenhouse Gas Inventory (GHGI) and other policy discussions; (2) develop estimates of episodic emissions; and (3) test new methods to characterize intermittent device emissions.

Colorado State University, Fort Collins, CO 80524

From 2013 to 2015, CSU conducted the first comprehensive national study of methane emissions from gathering compressor stations and processing plants as part of an EDF-organized emissions study. The CSU study included facility-level methane emissions measurements at 114 gathering compressor stations and 16 processing plants in 13 U.S. states. Methane emissions from gathering facilities were higher than expected, with 20 percent of the facilities exhibiting methane loss rates greater than 1%. The measurement results were used, along with a national estimate of gathering facility counts, to estimate total methane emissions from all U.S. gathering operations. The results showed that methane emissions from gathering was under-represented by a factor of eight in the GHGI. The GHGI was updated in 2016 (2014 data) to reflect the results of the CSU study, and included a revised gathering station count (4999 stations) and facility-level emission factor (43 kg/h) from the study. With these updates to the GHGI, gathering operations are now estimated to account for 27% of methane emissions from the natural gas supply chain. 

Unfortunately, constraints on the CSU gathering and processing (G&P) study did not allow for on-site measurement of individual emission sources. Because the GHGI utilizes per-device emission and activity factors to back-cast emissions, there is a pressing need to complement the prior study with detailed on-site, point-source measurements. Further, detailed knowledge of emission sources provides critical information for policy discussions related to emissions reductions, such as development of the Section 111(d) reporting requirements. Industry groups can utilize per-device emissions measurements to develop emissions reduction strategies, such as work currently underway by ONE Future™, a sponsor of this project. New emission measurements will inform new methane monitoring technologies.

Results of this study will identify device-level emission factors for the EPA GHGI, to support estimates of current methane emissions and to contribute to back-casting to GHGI’s 1992 baseline year. Additional elements of the study will provide data suitable for a broad range of emission modeling efforts. Emissions and activity data may also support modeling of non-methane emissions (such as volatile organic compounds), including life-cycle analyses, and (if regional differences are seen in activity data) regionalized models of emissions. The project will extend measurement science in the characterization of intermittent device emissions. Facility-level and device-level emission models will serve as a guide for methane mitigation efforts, such as utilizing low cost methane sensors for Leak Detection and Repair (LDAR) applications.

• The project established a group of nine industry partners who all operate gathering compressor stations, including some with upstream operations as well. These companies represent a national cross section of gathering facilities, and operate approximately 1,700 gathering compressor stations.
• Stack testing for methane entrained in exhaust emissions was accomplished using a novel in-stack tracer protocol. Instruments were checked and the data was analyzed. Results show good agreement estimating total flow relative to engine specifications and traditional stack methods. Testing was completed on 129 engines (including 81 lean-burn 4-stroke and 48 rich-burn 4-stroke engines). Due to lack of population, no turbines or 2-stroke engines were measured. Method and results were published in an additional methods-focused paper. (Vaughn TL, Luck B, Williams L, Marchese AJ, Zimmerle D (2021) Methane Exhaust Measurements at Gathering Compressor Stations in the United States. Environmental Science & Technology)
• Component counts were completed on 776 pieces of major equipment, including over 500 compressor units, resulting in field counts of over 85,000 components. Activity factors were published in the main paper and have been adopted by the GHGI for future modeling.
• A national emissions estimate was completed using equipment counts submitted by operators to the Greenhouse Gas Reporting Program (GHGRP) to scale up observed field measurements from this study. These 299 reports formed a strong basis for estimating national equipment counts.  Coupled with major equipment emission factors developed in the study, the study estimated total emissions from gathering and boosting stations in the USA. (Zimmerle D, Vaughn T, Luck B, Lauderdale T, Keen K, Harrison M, Marchese A, Williams L, Allen D (2020) Methane Emissions from Gathering Compressor Stations in the U.S. Environmental Science & Technology, 54(12):7552–7561.)
• Long-term (mean of 76 hours) pneumatic recordings were collected on 72 gas pneumatic controllers during the field campaign.  Data from these recordings identified failure rates that had not been previously identified, providing insights into how these controllers should be managed and maintained to reduce emissions.  For example, 25 of 45 intermittent controllers malfunctioned at some point during the recording period, a failure rate far higher than previously estimated. (Luck B, Zimmerle D, Vaughn T, Lauderdale T, Keen K, Harrison M, Marchese A, Williams L, Allen D (2019) Multiday Measurements of Pneumatic Controller Emissions Reveal the Frequency of Abnormal Emissions Behavior at Natural Gas Gathering Stations. Environmental Science & Technology Letters, 6(6):348–352.)
•  A final project close-out review was held with industry participants on 13 January 2020 (at Pioneer HQ in Dallas, TX).  The review covered all aspects of the project, including design of the study, primary results, learnings, and review of published results.
• All project data, and the final report, have been archived on CSU’s long-term repository, Mountain Scholar at https://mountainscholar.org/handle/10217/195489.  These include the final report and its three annexes: 
  • Pneumatic controller analysis
  • Compressor driver exhaust measurements 
  • Emission factors, station estimates, and national emissions

Project is completed.

$1,872,016

$474,727

NETL – Eric Smistad (eric.smistad@netl.doe.gov or 281-494-2619)
Colorado State University – Daniel Zimmerle (dan.zimmerle@colostate.edu or 970-581-9945)

Final Report [PDF] October 2019