Pressure-assisted flares, particularly pressure-assisted Multi-Point Ground Flares (MPGFs), have become an increasingly popular option for refineries, chemical plants, and other facilities needing a safe, effective control option for varying volumes of vent gas. From trickles of purge gas to millions of pounds of emergency venting, MPGFs provide exceptional flexibility and reliability. However, compliance with flare air quality regulations is challenging, especially for facilities operating pressure-assisted flare burners.
Prior to the recent amendments to the Refinery MACT, Ethylene MACT, MON, and HON RTRs, pressure-assisted flares by design could not meet exit velocity requirements as required under New Source Performance Standards (NSPS) or the general provisions of MACT Subpart A and were forced to operate under site-specific Alternative Means of Emission Limitation (AMEL) or Alternative Means of Control (AMOC) plans. Because these approvals were largely developed on a facility-by-facility basis, the resulting compliance obligations varied widely, creating a patchwork of requirements across the industry.
With the issuance of the aforementioned rule amendments, the U.S. Environmental Protection Agency (EPA) has taken significant steps to standardize the regulatory landscape for pressure-assisted flares. These finalized rules establish a more uniform set of operational requirements that are broadly applicable across facilities, aiming to improve both regulatory clarity and environmental performance.
Key operational requirements for pressure-assisted burners now include pilot flame presence monitoring to ensure that ignition is continuously maintained during flaring events. In addition, burner spacing design requirements or cross-lighting performance demonstrations must be met to ensure reliable flame propagation across burner stages. Facilities must also continuously monitor flare header pressure and the position of staging valves, which is critical for understanding how gas is distributed and combusted across different pressure zones within the flare. Perhaps most importantly, pressure-assisted flares now must meet a minimum 800 BTU/scf Net Heating Value of Combustion Zone (NHVcz) requirement at all times. This higher NHVcz limit is based on industry testing data collected and reviewed by EPA, who determined that a stable flame on a pressure-assisted burner almost always results in high combustion efficiency, and that above a NHVcz of 800 BTU/scf, all testing data showed stable flame operation.
Flare monitoring system requirements have also been finalized, and these provisions were particularly detailed. Facilities must prepare a monitoring plan for each Continuous Parameter Monitoring System (CPMS) used to comply with applicable provisions. These plans must reflect the required accuracy thresholds, calibration schedules, and verification procedures tailored to each type of CPMS in use, as required. It is critical that facilities are aware of these accuracy and calibration requirements, as proper documentation, such as accuracy guarantees from manufacturers or calibration certifications, must be maintained to demonstrate that all flare monitoring systems meet the applicable requirements.
In addition to these requirements, low-pressure stages of MPGFs must also remain in compliance with “traditional” flare requirements. As a result, compliance managers must balance a bevy of different requirements, some applicable only to certain burners or stages. In effect, a single MPGF system may be subject to multiple compliance frameworks simultaneously, depending on how each stage is operated and how the MPGF was initially permitted.
MACT CC and AMELs
Meeting the requirements of the amended rules can be complex, particularly during exceptional flaring events when vent gas conditions vary from typical operations. During emergency flaring, for example, vent gas composition and flow rate can vary significantly from typical operations, putting strain on the control systems and monitoring systems designed to ensure compliance. Turnarounds can further compliance, as the use of inert gases such as nitrogen during purging can dilute vent gas streams, potentially reducing NHVcz below acceptable levels. In fact, AMELs granted prior to the promulgation of the amendments typically included an LFLcz compliance alternative intended to accommodate these conditions, but this was notably absent from the final regulation.
Additionally, AMELs have also been granted with NHVcz limits lower than the 800 BTU/scf MACT CC requirement, based on site-specific testing data. Flares with AMELs have the option under the amended rules to continue to comply with their AMELs instead of the amendments for the high pressure stages. In fact, the rule language leaves the door open for facilities, both new and existing, to apply for AMELs today, allowing MPGF operators to possibly obtain alternative compliance limits that fit their facility’s needs.
If your facility operates an MPGF and is interested in reviewing compliance options, or if you are interested in learning more about MPGF regulations, please email Inaas Darrat or William Erickson from Trinity’s Chemical Sector Services (CSS) business line.
