In March 2024, the Environmental Protection Agency (EPA) published new regulations (NSPS OOOOb) aimed at curbing methane and volatile organic compound (VOC) emissions from the oil and gas industry. In this article, we dive into the requirements of NSPS OOOOb for centrifugal and reciprocating compressors used at onshore natural gas processing plants, compressor stations, and centralized production facilities.

Who Needs to Comply with NSPS OOOOb for Centrifugal & Reciprocating Compressors?

The EPA’s rule states that any compressor constructed, modified, or reconstructed after December 6, 2022, is an affected facility. However, EPA's rule lacks clarity regarding definitions and has not yet provided additional guidance. Based on our analysis:

• The rule applies to operators of centrifugal and reciprocating compressors.

• Screw, sliding vane, and liquid ring compressors are not considered centrifugal compressors

• It affects compressors manufactured after December 6, 2022.

• The manufacture date of the compressor typically differs from that of its associated driver or engine.

Operators should remain alert for any future guidance from the EPA that may clarify the rule’s language.

NSPS OOOOb Requirements for Centrifugal and Reciprocating Compressors

As part of the new regulation, compressors now have three options for wet/dry seal and rod packing vent routing:

• Route them to a control device with at least 95% efficiency. 

• Return them to the process. However, this option comes with a strict requirement. The design and operation of the process return system must be foolproof, eliminating any possibility of emissions escaping.

• Conduct routine volumetric monitoring

Centrifugal and Reciprocating Compressors Vent Limits and Monitoring

The rule establishes specific leak limits for each compressor type and requires facilities to maintain a low volumetric flow rate. These rates apply when compressors are in operating or standby mode.  

To ensure compliance, facilities must implement routine monitoring and repair practices for all compressor seals. Additionally, they are required to conduct initial monitoring and flow rate measurements within 8,760 operating hours of the effective date (May 7, 2024). 

Flexibility for Reciprocating Compressor Monitoring

The rule offers some flexibility for reciprocating compressors regarding the initial monitoring timeline. This flexibility allows facilities to align the initial monitoring with existing maintenance procedures, minimizing disruption. Facilities can choose the most convenient option for their maintenance schedule:

• Within 8,760 operating hours of the effective date.

• Whichever comes later: the last flow measurement or the most recent compressor rod packing replacement.

Repair Requirements for Compressor Vents

The EPA requires repair/overhaul of vents exceeding the allowed limit within 90 days. Following repairs, a verification of success must be completed within 15 days. The EPA allows a delay of repair justification if deemed infeasible due to safety concerns, vent blowdown requirements, or the next scheduled shutdown (whichever comes first). Additionally, a delay is allowed if the specific repair part is unavailable, but the part must be ordered within 10 days. Because most compressors will require a vent blowdown to replace packing or seals, the 15-day verification following repair will involve close coordination between equipment vendors, in-house mechanics, environmental departments, and contractors.   

Recordkeeping and Reporting Requirements

NSPS OOOOb requires facilities to implement a reporting system for their compressors. There are two options to choose from:

• Closed-Vent Systems: Facilities utilizing closed-vent systems for their compressors must document and report on their operation. This includes maintaining records of each inspection, noting any emissions found, and recording the repair date or anticipated repair date if a fix is delayed.

• Performance-Based Standard:  Alternatively, facilities can choose a performance-based standard for compressor seals. This approach requires tracking the total annual operating hours of each compressor and recording the results of any seal measurements.  Any measurements exceeding the allowed threshold and the repair details (date and time) must be reported. If a repair is delayed due to parts availability, the entire process needs to be documented, including the reason for the delay and the anticipated repair date.

Questions? Connect with Our Air Compliance Specialists. 

Trihydro’s air quality and regulatory specialists remain current on changing regulations to support you in maintaining compliant operations and reporting. We can help you set up a notification response program, conduct proactive monitoring, and assist in understanding the overall implications of NSPS OOOOb compliance. 

Contact us to discuss your NSPS OOOOb compliance strategy.