A105-14
Analysis of Methane Emissions from San Francisco Bay Area Refineries

Thursday, 10 December 2020: 18:09
Virtual
Sally Newman1, Abhinav Guha1, Linda Duca2, William Saltz2, Steve Conley3, Mackenzie Smith4, Andrew K Thorpe5, Riley M Duren6, Kelsey Foster7, Daniel Cusworth5, Arthur Valla2 and Philip T Martien1, (1)Bay Area Air Quality Management District, San Francisco, CA, United States, (2)Bay Area Air Quality Management District, San Francisco, United States, (3)Scientific Aviation, Boulder, CO, United States, (4)Scientific Aviation Inc., Boulder, CO, United States, (5)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, (6)University of Arizona, Tucson, AZ, United States, (7)Stanford University, Stanford, United States
Abstract:
The Bay Area Air Quality Management District (BAAQMD), the San Francisco Bay Area’s (SFBA) air quality regulatory agency, has set a goal to reduce the region’s greenhouse gas (GHG) emissions 80% below 1990 levels by 2050, consistent with California’s climate goals. To support the agency’s climate action programs and rule-making efforts, along with implementing the control strategies laid out in the multi-pollutant 2017 Clean Air Plan, the BAAQMD maintains a regional bottom-up GHG emissions inventory, which is derived using a combination of activity data and emission factors.

To support the 2017 Plan, the Air District is employing data collected using multiple methods to refine its methane (CH4) emissions inventory. Facility-level emissions determinations using aircraft-based top-down measurements circling refineries have shown large discrepancies when compared with bottom-up activity-based inventories and self-reported emissions. Indeed, measured CH4 emission rates determined for the five SFBA refineries are 4 to 23 times larger than those from reported estimates. The measurement-based assessment results in a 10-fold increase in the revised refinery sector CH4 estimates. Thus, these measurements suggest large underestimation of CH4 emissions from refineries in the inventories. The airborne imaging spectrometer AVIRIS-NG mapped CH4 plumes emanating from hydrogen (H2) production plants at two SFBA refineries. H2 gas is an essential feedstock in most petrochemical processes and is produced in large volumes at refineries via steam reformation that uses natural gas (>80% CH4). Depending on the type of abatement technology applied and associated gas flow/vent schematics, there can be residual CH4 in the product gas following this large-scale synthesis. We used refinery-reported data on vented H2 volumes and vent gas chemical composition to calculate CH4 emission rate averages from H2 production units at three SFBA refineries that have atmospheric vents. Our analysis suggests that a third of the facility-wide emissions determinations by the airborne-based mass-balance method may be derived from emissions from H2 production plants at refineries. These data will contribute important information toward our on-going rule-making efforts to reduce GHG emissions from these facilities.

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