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Characteristics of Gathering and Boosting Stations
Project Number
DE-FE0029068
Last Reviewed Dated
Goal

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.

Performer

Colorado State University, Fort Collins, CO 80524

Background

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.

Impact

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.

Accomplishments (most recent listed first)
  • 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 will be published in an additional methods-focused paper.
  • 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 will be published in the main paper.
  • 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 will form a strong basis for estimating national equipment counts, which will then be combined with emissions factors from this study to estimate total emissions from gathering and boosting stations.
  • Long-term pneumatic recordings were corrected for non-zero values observed using a battery of tests performed on the high-flow instrument utilized in the study to determine the lower detection limit of the instrument in field-like conditions. Testing was performed at the Methane Emissions Test and Evaluation Center (METEC) at CSU, an ARPA-E MONITOR funded facility. https://energy.colostate.edu/metec/
  • The team completes biweekly discussions with the study partners’ technical review committee.
  • A final face-to-face meeting with industry participants was completed on December 6, 2018, during which major results were presented and discussed. Key results for all aspects of the project are generally finalized, with a few remaining adjustments to the national model required prior to drafting papers.
  • Due to the number of corrections on the pneumatic recordings, the team has decided to submit the data and results to the “Letters” section of Environmental Science & Technology (ES&T), and to potentially follow up with additional measurements in the spring before recommending final emission factors for pneumatic controllers.
  • Manuscripts discussing results of pneumatic measurements, exhaust measurements and the overall national model are expected to be submitted for publication in January 2019, and a final report will be completed by end of February 2019.
Current Status

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.

Project Start
Project End
DOE Contribution

$1,872,016

Performer Contribution

$474,727

Contact Information

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