In August of 2012, U.S. EPA announced that Flaring Efficiency would be targeted as part of an enforcement initiative. EPA investigations determined that flares at several facilities were improperly monitored and/or operated in a way that resulted in a low combustion efficiency, violating federal law that requires that pollution control equipment be operated using good air pollution control practices to minimize emissions. While flares have long been subject to EPA enforcement in the refining and chemical industries, this enforcement initiative focuses specifically on low flaring efficiency and the resulting additional unaccounted emissions of toxic air pollutants and volatile organic compounds (VOCs).
Current federal requirements for flares, found in the New Source Performance Standards (NSPS) at 40 CFR 60.18 and National Emission Standards for Hazardous Air Pollutants (NESHAP) at 40 CFR 63.11, reflect flare performance studies conducted in the 1980s by EPA. These studies found that a suitable combustion efficiency (>98% conversion of organic compounds to CO2) was dependent on flares operating within “their stable flame envelope.” The requirements in §60.18 and §63.11 seek to restrict flare operation to maintain the “stable flame envelope” and thus ensure an appropriate combustion efficiency. The requirements are as follows:
- Flares must be designed and operated with no visible emissions;
- Flares must be operated with a flame present at all times;
- Vent gas sent to the flare must have a net heating value greater than specific thresholds or equal to 300 BTU per standard cubic foot (BTU/scf) (if the flare is steam- or air-assisted) or greater than or equal to 200 BTU/scf (if the flare is non-assisted); and
- Flares must be designed for and operated with an exit velocity less than 60 feet per second (ft/sec) (with some exceptions).
In the past, flare operators often focused on ensuring the flare pilot was always lit and preventing a smoking flare. Under the current enforcement initiative, EPA shifted the focus to factors which negatively affect flare combustion efficiency, including flame quenching in the combustion zone, caused by over-steaming/over-aeration, and a low heating value in vent gas. Assisted flares utilize steam or air to protect the flare tip from overheating and cultivate mixing which allows for proper combustion of VOCs and minimize visible emissions from the flare; however too much steam or air can lower the vent stream heating value and lead to a low combustion efficiency. In the same vein, low net heating value of vent gas sent to the flare also leads to a low combustion efficiency.
To prepare for future EPA inspections, facilities have several options for identifying and addressing low combustion efficiencies including, but not limited to:
- Understanding and/or monitoring vent stream heating value for all flare venting scenarios;
- Determining the net heating value of the combustion zone (NHVCZ) gas, a parameter EPA identifies as a better indicator of combustion efficiency that heating value alone;
- Adjusting steam-to-vent gas ratio to prevent over-steaming;
- Adding supplemental gas to vent gas with low net heating value; and
- Limiting flare usage strictly to emergency situations
If you need assistance evaluating the flares at your facility, please contact Ms. Inaas Darrat at (713) 552-1371 or reach out to your local Trinity office at (800) 229-6655.