2.2 Refinery Fugitive Emissions
Categories 17, 18, 19, and 2559
2.2.1 Introduction
Categories 17, 18, 19, and 2559 account for refinery fugitive emissions from sealed equipment at valves and flanges, pump and compressor seals, pressure relief valves, and miscellaneous others, respectively.
These emissions are treated as point sources and are unique to each refinery. Emissions include volatile organic compound (VOC) emissions. Emissions occur from process equipment whenever components such as valves, flanges, pumps, compressors, and pressure relief valves (PRVs) leak due to seal failure. These emissions generally occur randomly and are difficult to predict occurrences. Of these three categories, valve and flange leaks account for the bulk of total fugitive emissions while pressure relief valves account for the smallest amount of total fugitive emissions.
This chapter also accounts for miscellaneous others, category 2559, which are emissions not accounted for in other refinery categories.
2.2.2 Methodology
Point Sources are operations that emit air pollution into the atmosphere at a fixed location within a facility, for which the Air District has issued a permit to operate, e.g. refinery cooling towers. These could also be a collection of similar equipment / sources located across multiple facilities, e.g. reciprocating engines.
During the permit to operate (PTO) issuance process, the BAAQMD collects information from the operating facility and/or determines from published literature, e.g. EPA’s AP-42, characteristics of a source including maximum throughput, emission factors for emitted pollutants, and control factors associated with downstream abatement devices. These characteristics are then stored for future use in the BAAQMD’s internal database. Facilities that hold a permit to operate are required to renew this permit periodically (this period varies based on facility and source type). Upon renewal, the facilities are requested to provide any updates to source characteristics as well as the source throughput for the last 12 months. This throughput, in combination with the emission factors and controls factors stored in the internal database, are used to estimate annual emissions at the source level. These source level emissions are then sorted and aggregated into categories.
Further speciation and quality assurance of emissions are performed as a part of the inventory process. The BAAQMD staff also perform a systematic crosswalk between CEPAM’s source category classification (Emission Inventory Code - EICs) and the District’s source category classification (category identification number - cat_ids), which ensures consistency in the annual emissions reporting process (CEIDARS) to California Air Resources Board. The last part of the inventory development process includes forecasting and back casting, and aggregation into sub-sectors and sectors for documentation purposes. For those years where no data is available, emissions data are backcasted to year-1990, as well as forecasted to year-2040 using either interpolation or another mathematical approach (see Trends section). Finally, emissions trends spanning from year 1990-2040 for each category and pollutant are evaluated for anomalies that are then investigated and addressed.
Categories 17-19 are considered point source categories and follow the above methodology for emissions estimates. To limit and reduce emissions from these categories, District’s Regulation 8, Rule 18 (Equipment Leaks), Rule 28 (Episodic Releases From Pressure Relief Devices at Petroleum Refineries and Chemical Plants)3 limit fugitives and episodic emissions from source devices at refineries and chemical manufacturing plants.
The petroleum refineries are periodically surveyed for the number of mechanical components utilized in an oil refining process. These components include valves, PRVs, pumps, and compressor seals. Individual types of components are summed up and emissions are calculated based on throughputs and specific emission factors.
Emission information from numerous sources is grouped into the above mentioned categories. EPA’s AP-42, Chapter 54 contains description of petroleum refining processes and emission factors. Criteria pollutant, mainly total organic compounds, and greenhouse gas emissions, including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are produced during refining processes. Since refinery emissions are part of point sources, criteria pollutants as well as greenhouse gas data are obtained from the refinery plant as part of the Bay Area Air District annual permit renewal process.
Category 2559 emissions are a catch all for those refinery emissions not captured by other categories. This category does not have emissions in base year 2015. Due to District’s Regulation 12-15 (Petroleum Refinery Emissions Tracking Rule) passed in year 2018, where refineries are required to track air emissions and crude oil composition characteristics over time and to establish air monitoring systems to provide air quality data along refinery boundaries, this category started accounting for emissions in year 2019.
2.2.3 Changes in Methodology
There are no changes in the methodology to estimate emissions in the current base year inventory compared to the previous base year inventory (year 2011).
2.2.4 Emissions
A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.
2.2.5 Trends
In general, emissions increase as throughputs increase. In addition to usage changes, new installations also increase the emissions.
(a) Historical Emissions / History
Historical emissions for point source emissions are derived from source-specific throughputs provided by the permitted facility, compiled/reported emission factors, and regulation-based control factors. This information is archived in the BAAQMD’s internal database which is queried to retrieve the data for historical and current years. Interpolation techniques to account for missing data are used when necessary, this is the case for years 1991-1992. Historical changes in fugitive emissions in the Bay Area have been due to installation of newer process units that supplement rather than replace old process units. Category 2559 contains no historical emissions as its emissions accounting started in year 2019, after the passage of Regulation 12-15. There are no historical emissions accounted for this category in the current base year inventory.
(b) Future Projections / Growth
Forecasting of point source emissions is done based on calculations as shown in the equation below using recently updated growth profiles and a base year of 2020. The growth profiles for the current base year inventory have been verified and updated to represent the most likely surrogate for growing emissions for a given category up to year 2040. Forecasting for point source emissions includes impact of in-place regulations, but does not include estimation of controls that will theoretically be implemented as part of future policy emission targets or proposed regulation and legislation.
\[ \text{PE} = \text{Gr} * \text{Ci} * \text{Ei} \] \(PE\) = projected emissions of pollutant i in a future year
\(Gr\) = growth rate by economic profile of industry or population
\(Ci\) = control factor of pollutant i based on adopted rules and regulations
\(Ei\) = base year emissions of pollutant i
Projected growth for all refinery related categories was based on the even extrapolation of California Annual Operable Atmospheric Crude Oil Distillation Capacity reduction from 2010 to 2020, i.e., it’s assumed a 0.67% decrease annually from 2021 to 2040. The data used in the extrapolation is taken from US Energy Information Administration website5. The decrease is primarily driven by the shift to further increase fuel efficiency of vehicles through the U.S. Department of Transportation’s National Highway Traffic Safety Administration Corporate Average Fuel Economy (CAFÉ) standards as well as steady transition to electric vehicles and other alternative fuels (hydrogen fuel cell and others) in the California market.
Additionally, efforts are being made to streamline and standardize rules and regulations. Any subsequent refinement in [Rule 8-18 and Rule 8-28]1 due to this streamlining should further reduce emissions in these categories. It is expected that fugitive emissions will not increase significantly in future after new units are built to produce reformulated gasoline.
2.2.6 Uncertainties
Throughputs for these categories are reported via permit system requirement on a year by year basis and are assumed to reflect the most current data available at the time. Throughput data that are taken based on source test is considered the most accurate, followed by engineering calculations such as mass/material balance, and then published data via literature such as AP-42. The emission factors are estimated using historical data and could change or be improved as new data is published.
2.2.7 Contact
Author: Tan Dinh
Reviewer: Abhinav Guha, Yuan Du
Last Update: November 06, 2023
2.2.8 References & Footnotes
BAAQMD. Rules; [accessed 2023 March 07]. https://www.baaqmd.gov/rules-and-compliance/current-rules↩︎
USEPA. AP-42; [accessed 2023 March 07]. https://www.epa.gov/air-emissions-factors-and-quantification/ap-42-compilation-air-emissions-factors↩︎
US Energy Information Administration. Data ; [accessed 2023 March 07]. https://www.eia.gov/dnav/pet/pet_pnp_cap1_dcu_SCA_a.htm↩︎