PR-312-16202-R02 GHG Emission Factor Development for Natural Gas Compressors

The U.S. EPA Greenhouse Gas (GHG) Reporting Program (GHGRP) requires compressor stations and underground storage facilities to measure compressor vent, rod packing, and seal emissions for facilities subject to 40 CFR, Part 98, Subpart W. The objective of the project is to gather and evaluate 2011 - 2016 Subpart W compressor vent and seal methane emissions data from site measurements, and present final results of an analysis to develop methane Emission Factors (EFs) based on these data. The EFs and analysis of relative contribution from different sources can be used: (1) as alternatives to current emission factors for compressor methane emissions used for Transmission and Storage (T&S) operations in EPA's annual GHG inventory; (2) to provide an EF based emission estimate for Subpart W that replaces ongoing annual GHGRP vent measurements; and (3) to document the relative contribution of different compressor leak/seal sources and support alternative leak mitigation strategies. Comparisons of the EPA Annual GHG Inventory EFs to Subpart W based EFs in this report show consistently lower compressor emissions than estimates based on historical data or reports. Large leaks, which stem from less than 3% of the compressor measurements, increase the EFs by 26% to 194%, thus greatly impacting the EF results. Alternative EFs are provided for transmission and storage compressor methane emissions.