The US Environmental Protection Agency (EPA) 40 CFR Part 60 Subpart OOOO, or Quad O, is a federal regulation under the Clean Air Act for reducing harmful air quality emissions from oil and gas facilities.
The EPA issued a final rule effective May 7, 2024, containing new source performance standards (NSPS) regulating greenhouse gases (GHGs) and volatile organic compound (VOC) emissions for the oil and gas industry. It also finalized guidelines for states to follow in developing their emission reduction standards for limiting fugitive emissions from existing sources.
In this blog, we will focus primarily on the recent OOOOb update, which includes new standards covering both wet- and dry-seal centrifugal compressors that have limits on the seal flow rate. We’ll also cover new limits to leaks from reciprocating compressors, as well as the changes to state guidelines for compressors in the OOOOc update.
Finally, we’ll discuss how oil & gas companies can benefit from mass thermal flow meter technology to meet the finalized Quad O regulations.
Wet Seal Centrifugal Compressors
The Quad O requirements for gas compressors found in OOOOb require wet-seal centrifugal compressor stations to capture and route emissions from the wet-seal fluid degassing system to a control device or a process. Self-contained wet seal compressors, in general, send their gas back to the system process.
OOOOb requires that the vent rate for self-contained wet seal centrifugal compressors must not exceed 3 standard cubic feet per minute (scfm) per seal. If the leak exceeds this limit, the seal must be repaired and a confirmatory leak measurement performed after the repair. For those located on Alaska North Slope, the limit changes to 9 scfm per compressor seal.
In addition, an annual flow rate of the wet seal must be measured on or before 8,760 hours of operation to detect leaks. Flow rate measurements can be taken either with a temporary or a permanent flow meter or a high-volume sampler.
Centrifugal compressors located at a well site, rather than a centralized production facility, are exempt from these rules.
Dry Seal Centrifugal Compressors – A New Emission Source
Dry seal centrifugal compressors are a new emission source regulated by OOOOb. The dry seal centrifugal compressor gas vent flow rate must not exceed 10 scfm per seal. If the leak exceeds this limit, the seal must be repaired and a confirmatory leak measurement must be performed after the repair.
To detect leaks, an annual dry seal compressor flow rate must be measured on or before 8,760 hours of operation. Flow rate measurements can be accomplished with either a temporary or permanent flow meter or a high-volume sampler.
Dry seal compressors can elect to capture and route emissions with a control device that is at least 95% efficient (e.g., a flare).
Centrifugal compressors located at a well site are exempt from these rules.
Quad O Requirements for Reciprocating Compressors
In reciprocating compressors, methane can leak from valves, flanges, and fittings, but the most significant source of gas leakage is the piston-rod packing. From there, leaking gases are vented to the atmosphere through packing vents on the flange.
OOOOb places a flow limit on the packing vents for reciprocating compressors so that rod packing leaks cannot exceed 2 scfm per individual cylinder. If the leak exceeds this flow rate, the rod packing must be replaced or repaired. A confirmatory leak measurement is required after a repair and a follow-up measurement of the rod packing seal is required after repair/replacement.
As an alternative to periodic measurement, the rod packing seal can be sent through a closed vent system either to a process, such as a fuel gas system or to an emission control device that is at least 95% efficient, such as a flare.
Annual flow rate monitoring of rod packing seal leaks is required. Seal flow rate measurements must be conducted on or before 8,760 hours of operation, and a temporary meter or high-volume sampler may be used to quantify leak rates.
Reciprocating compressors located at a well site are exempt from these rules.
State Quad O Updates for Gas Compressors
Under OOOOc, each state must submit its plan to reduce emissions. State plans must be at least as proactive as the EPA state model plan, but they could include additional VOC and methane emission standards. However, until each plan has been approved and implemented, operators will not know the full impact on gas compressors for that state.
Flow Meters for Quad O Emissions Reporting
Flow meters can help oil and natural gas companies meet the emissions reporting requirements of Quad O to improve their impact on the environment and avoid fines due to methane and VOC emissions. They can also help prevent misreporting, such as identifying emissions issues due to packing vent leakage and providing accurate emissions data during a blowdown event.
Fox Thermal's flow meter models FT4A and FT4X, are specially designed for gas applications. These models feature the digital DDC Sensor and Gas-SelectX® menus which are particularly beneficial for gas applications. They also come with the CAL-V™ feature so that operators can verify NIST-traceable meter functionality at any time in the field.
Gas-SelectX® gives operators the ability to set the meter to measure specific mixes of gases. It allows the meter to measure different gases and gas percentages more accurately. The user can choose from standard lists of gases or mix any to create a custom gas mix specifically for their application, and easily change the gas composition in the field.
Made for Oil & Gas Monitoring
The FT4A and the FT4X are most suitable for monitoring natural gas sources for Quad O compliance. These two models are pre-calibrated with an expanded Oil & Gas menu in Gas-SelectX®.
Naturally occurring gas from oil fields, commonly referred to as Associated Gas, may have a different percentage of gas constituents in its composition. Operators can use the Mixed Gas or Oil & Gas Menu in Gas-SelectX® to program the correct percentages of the natural gas constituents into the flow meter.
Advanced Data Logger for Emissions Reporting
The FT4X offers further value with a built-in advanced 7-year data logger. The feature includes a configuration log that lists how the meter is set up for the application, along with an event log that shows any changes to the meter settings with date/time stamps.
This creates a detailed record of what has happened in the meter since installation, whether or not any changes have been made, and/or if there has been a trigger to the alarms for conditions that go outside of the acceptable range for the flow measurement point.
These logs allow the user to prove that there has been no manipulation of the meter's programming to make the meter misreport flow data. Such records can help operators report their emissions data to remain compliant with Quad O.
Get Support Meeting Quad O Gas Compressor Regulations
The newly finalized Quad O gas compressor regulations are designed to minimize methane leakage, a key climate objective. Gas companies that proactively measure and monitor leaks will not only reduce their environmental impact, but also save money on fines and wasted fuel, increase safety for onsite workers, and prevent major repairs.
have questions about OOOOb/c regulations? Speak with your local Subject matter Expert today.