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U.S. EPA Issues Final Flare Emission Factor Decision: NOx Emission Factor Unchanged

Posted: April 23rd, 2015

Author: All4 Staff 

In September 2014, we alerted you to U.S. EPA’s proposal to significantly increase the emission factors for various pollutants, most notably nitrogen oxides (NOX), emitted from industrial flares.  As you may recall…

  • In May 2013, environmental groups filed a lawsuit against U.S. EPA for failure to perform compulsory duties pursuant to the Clean Air Act (CAA) to review, and, if necessary, revise the emission factors for volatile organic compounds (VOC) for flares, liquid storage tanks, and wastewater collection, treatment, and storage systems. 
  • As a result of the litigation, in early 2014, U.S. EPA entered into a consent decree stipulating that they were going to review and, if necessary, propose new emission factors for VOC for the aforementioned sources.
  • In August 2014, based largely on data collected during the 2011 Refinery Information Collection Request (ICR), the data referenced in the litigation, and other test data available to U.S. EPA, U.S. EPA decided to propose a new VOC emission factor for flares, as well as other emission factors for refinery operations and pollutants that were not specifically covered by the 2014 consent decree.

Since last August, U.S. EPA has received hundreds of comments from environmental groups and industry regarding the proposed emission factor revision.  On April 20, 2015, U.S. EPA concluded that a revision to the NOX emission factor published in Section 13.5 of AP-42 (Compilation of Air Pollutant Emission Factors) was not necessary.  As you can see in the table below, U.S. EPA has published a new emission factor for VOC, has reduced the published emission factor for carbon monoxide (CO), and has not changed the emission factors for total hydrocarbons (THC) or NOX.

Specifically regarding flares, U.S. EPA issued a statement saying, “Based on our review of NOX emissions data for flares and additional information received after proposal, we have determined that the data was not adequate to support revising the NOX emissions factor for flares.  Based on comments received, U.S. EPA determined that the NOX data used for the proposal contained certain flaws that rendered the data quality suspect.”  In addition to the revised NOX emission factor, affected facilities should also take note of the new VOC emission factor.  According to AP-42, VOC emissions were previously assumed to be negligible.  It is possible that increased VOC emissions could have impacts in emissions reporting and permitting decisions going forward.

In order to assist Petroleum Refineries in estimating emissions from various refinery operations, the U.S. EPA Office of Air Quality Planning and Standards (OAQPS) has published a revised Emissions Estimation Protocol for Petroleum Refineries” (Refinery Protocol).  U.S. EPA considers “the Refinery Protocol to provide site-specific emissions inventory guidance that will result in more accurate and complete emissions inventories.”  Sections 1, 5, and 6 of the Refinery Protocol has been updated with these new emission factors.

U.S. EPA has also published new emission factors, or emissions estimation methodologies, for certain refinery operations and pollutants that were not covered by the original consent decree.  These pollutants and refinery operations include: NOX, CO, and THC emissions from Sulfur Recovery Units, THC emissions from Catalytic Reforming Units, NOX emissions from Hydrogen Plants, and hydrogen cyanide (HCN) emissions from Fluid Catalytic Cracking Units.  AP-42 Sections 5.1 and 8.13 have been updated to include these new factors. Please note that HCN emissions are potentially required to be reported under the jurisdiction both the Toxic Release Inventory (TRI) and the National Emissions Inventory (NEI) reporting programs.  The revised emission factor for HCN could impact the TRI and/or NEI reporting obligations for facilities that use Fluid Catalytic Cracking Units.

More information, including U.S. EPA’s formal review of available documents and test reports used for developing these emission factors, can be found here.


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