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.
Data analysis is complete except for minor finalization to the national model. Paper drafts are underway, and will be sent to participants for review by early January 2019. Submission to journals will follow.