Updates to AP-42 Emission Factors for Flares and Other Refinery Process Units



On April 20, 2015, the United States Environmental Protection Agency (USEPA) issued final revisions to various emission factors used to estimate emissions for flares and other refinery process units.

These updates were made in order to fulfill the requirements of a consent decree between USEPA and Air Alliance Houston, Community In-Power and Development Association, Inc. (CIDA), Louisiana Bucket Brigade, and Texas Environmental Justice Advocacy Services (TEJAS) (collectively, "Plaintiffs"). The consent decree was brought about as a result of the lawsuit Air Alliance Houston, et al. v. McCarthy, which was filed against USEPA by the Plaintiffs on May 1, 2013. The Plaintiffs stated that USEPA had not fulfilled their requirement to review and, if necessary, revise emission factors at least once every three years; additionally, the Plaintiffs provided reports which supported the idea that VOC emissions from industrial flares, liquid storage tanks, and wastewater collection, treatment, and storage systems can be higher than those estimated using the emission factors presented in AP-42.

After conducting a review of the emission factors and emissions estimation methodologies, USEPA made several revisions and additions to AP-42 and other emission documents, including:

  • Addition of the 0.43 g HCN/kg coke burn (or 0.43 lb HCN/103 lb coke burn) emission factor for fluid catalytic cracking units in AP-42 Section 5.1, Petroleum Refining.
  • Addition of the 0.0007 kg THC/103 L feed (or 0.24 lb THC/103 bbl feed) emission factor for catalytic reforming units in AP-42 Section 5.1, Petroleum Refining.
  • Addition of the 0.081 lb NOx/MMBtu emission factor for hydrogen plants in AP-42 Section 5.1, Petroleum Refining.
  • Updates to the NOx, CO, and THC emission factors for sulfur recovery units and modifications to Table 8.13-1 in AP-42 Section 8.13, Sulfur Recovery.
  • Addition of the 0.57 lb VOC/MMBtu emission factor and revision to the CO emission factor from 0.37 lb CO/MMBtu to 0.31 lb CO/MMBtu for flares in AP-42 Section 13.5, Industrial Flares.
  • Revised Emissions Estimation Protocol for Petroleum Refineries document in order to add guidance on the inclusion of startup, shutdown, and malfunction event emissions in facility emission estimates, as well as include updated emission factors and a new section on estimating emissions from delayed coking units.

In addition to these updates, USEPA reviewed AP-42 Section 7.1, Organic Liquid Storage Tanks, and AP-42 Section 4.3, Waste Water Collection, Treatment and Storage, and found that no updates were necessary to any of the emission factors in these sections, but that using site-specific variables and information in the equations is crucial to obtaining accurate emission estimates.

More information on these updates and the consent decree can be found on the EPA's website here. The updated emission factors can also be found in AP-42 here.