2.1 General Refinery Emissions

Categories 10 - 16

2.1.1 Introduction

Categories 10 through 16 account for various emissions from general refinery processes in the Bay Area.

The emissions reflected herein include all five criteria pollutants (PM, VOC, NO_x, SO_x, CO). Petroleum refining involves an array of equipment which processes crude oil into consumable products such as fuel gas, lube oil, and grease. The emissions that are generated as a byproduct from these processes make up the petroleum refining emissions categories as listed below. Emissions reported are those generated via basic refining processes/devices and do not include emissions from refinery fugitives, storage units, and combustion processes (other than flares and blow down systems) which are accounted for in other categories of the emission inventory report.

Category 10 accounts for emissions from refining processes that involve chemical reactions, such as, but not limited to cracking, polymerization, and reforming. Significant amounts of nitrogen oxide (NO_x), sulfur oxide (SO_x), carbon monoxide (CO), and particulate matter (PM) emissions are produced during catalytic cracking and coking operations.

Category 11 includes emissions from all permitted refinery oil/water separation equipment and fugitive emissions from process drains. This category also contains emissions from clarifiers and dissolved air flotation systems.

Category 12 accounts for emissions from treatment of wastewater at oil refineries.

Category 13 contains emissions from cooling systems. Emissions from cooling towers consist of fugitive VOCs and dissolved gases (such as hydrogen sulfide and ammonia) which are leaked through heat exchangers into cooling water. The contaminants are then vaporized into the atmosphere at the cooling tower.

Category 14 includes emissions from vacuum producing systems. Vacuum systems are used primarily to distill heavy crude residues which cannot be distilled at atmospheric pressure.

Category 15 accounts for all refinery process gas (combustion) emissions from flares and blow down systems. Refinery flares can emit large quantities of organics, sulfur dioxide and carbon monoxide as well as greenhouse gases.

Category 16 includes emissions from all other refinery processes not covered in category 15. Emissions of organic compounds and greenhouse gases from storage tanks, sulfur recovery units, and combustion processes are included in chapters/sections on Petroleum Products, Chemical Plants, and Turbines, respectively. The processes in this category include distillation, hydrogen manufacturing plants, fuel blending. Coke loading and storage facilities account for most of the particulate emissions in this category.

2.1.2 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. The categories (10-16) captured in this Chapter are considered point source categories and follow the above methodology for emissions estimates.

The refineries in the Bay Area are permitted by the District under the Title V program, a Federally-mandated operating permit program for major sources of air pollution, and the refinery emissions are regulated by the District as well. Over the years, the District has enacted regulations to limit emissions from refinery sources. Below is a list of regulations¹ enacted by the District to limit emissions from refinery sources:

• Regulation 6, Rule 5: Particulate Emissions from Refinery Fluidized Catalytic Cracking Units
• Regulation 8, Rule 1: General Provisions
• Regulation 8, Rule 5: Storage of Organic Liquids
• Regulation 8, Rule 6: Organic Liquid Bulk Terminals and Bulk Plants
• Regulation 8, Rule 7: Gasoline Dispensing Facilities
• Regulation 8, Rule 8: Wastewater Collection and Separation Systems
• Regulation 8, Rule 9: Vacuum Producing Systems
• Regulation 8, Rule 10: Process Vessel Depressurization
• Regulation 8, Rule 18: Equipment Leaks
• Regulation 8, Rule 28: Episodic Releases From Pressure Relief Devices at Refineries and Chemical Plants
• Regulation 8, Rule 33: Gasoline Bulk Terminals and Gasoline Cargo Tanks
• Regulation 8, Rule 39: Gasoline Bulk Plants and Gasoline Cargo Tanks
• Regulation 8, Rule 44: Marine Tank Vessel Operations
• Regulation 8, Rule 53: Vacuum Truck Operation
• Regulation 9, Rule 1: Sulfur Dioxide
• Regulation 9, Rule 10: Boilers, Steam Generators and Process Heaters in Refineries
• Regulation 11, Rule 10: Hexavalent Chromium Emissions From All Cooling Towers and Total Hydrocarbon Emissions From Refinery Cooling Towers
• Regulation 12, Rule 11: Flare Monitoring at Refineries
• Regulation 12, Rule 12: Flares at Refineries
• Regulation 12, Rule 15: Refining Emissions Tracking

Regulation 12, Rules 11 and 12, pertain to flare monitoring and flare minimization plan respectively at Petroleum Refineries. Though the rules does not mandate reductions, District staff has found that flaring activities at the five Bay Area refineries have dropped dramatically over the past years because refiners have looked more closely both at monitoring and the feasibility of flaring reductions. This results in a significant emission reduction that cannot be directly attributed to the rules, but has been and will ultimately be reflected in the emissions.

2.1.3 Changes in Methodology

There are no changes in the methodology to estimate emissions in the current base year inventory as compared to the previous base year inventory (year 2011).

2.1.4 Emissions

A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.

2.1.5 Trends

Due to enactment of District regulations and modernization of refinery equipment in accordance with Title V permits, refinery emissions have been trending down over the years. Most notably, in 2010, SO_x decreased significantly as a result of an abatement device installation at Valero refinery. Over 90% of SO_x emissions were reduced at Valero refinery from prior years. Other reductions worthy of mention that helped to reduce air pollutant emissions include the flare minimization rule¹ and the requirement of continuous emission monitoring devices to monitor and prevent unanticipated emission of a criteria pollutant, toxic air contaminant, and/or greenhouse gas into the atmosphere.

(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.

In 2010, SO_x decreased significantly as a result of an abatement device installation at Valero refinery. Over 90% of SO_x emissions were reduced at Valero refinery from prior years.

(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 website². 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.

Future flare emissions are difficult to predict, since they are predicated on emergencies and the nature of emergencies which are unknown and unpredictable. However, with the recent passage of refinery flare monitoring and flare minimization plan requirements, flare emissions are expected to remain constant as long as there are no large upset in refinery processes that would warrant increase in flaring activities.

2.1.6 Uncertainties

Throughputs for these categories are reported by facility 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-42². The emission factor is estimated using historical data and could change or be improved as new data is published.

A step increase in TOG emissions for these categories may be seen for the periods of 2000-2001 and 2007-2008. This is due to a sustained Air District effort to gradually include and update methane emissions for various source types over these two periods of time. For years 1990-2008, high uncertainty in the TOG emissions estimates is expected; further refinement in backcasting of historical TOG emissions is planned in future inventory updates.

2.1.7 Contact

Author: Tan Dinh

Reviewer: Abhinav Guha, Yuan Du

Last Update: November 06, 2023

2.1.8 References & Footnotes

---

1. BAAQMD. Refinery Rules; [accessed 2023 March 07]. https://www.baaqmd.gov/rules-and-compliance/rule-development/refinery-rules-definitions↩︎

2. US Energy Information Administration. Data ; [accessed 2023 March 07]. https://www.eia.gov/dnav/pet/pet_pnp_cap1_dcu_SCA_a.htm↩︎