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Proposed Changes to AP-42 to Impact Liquid Storage Tanks

In what will likely have significant impacts on the petroleum industry, the U.S. Environmental Protection Agency (EPA) is proposing revisions to AP-42, Chapter 7. AP-42, the Compilation of Air Pollutant Emission Factors, is the primary compilation of the EPA's emission factor information. AP-42 contains emissions factors and process information for over 200 air pollution source categories (specific industry sector or group).

The proposed changes are focused on Chapter 7, Section 7.1 of AP-42. Section 7.1 presents emissions estimating methodologies for storage tanks of various types and operating conditions. The EPA notes that “the methodologies are intended for storage tanks that are properly maintained and in normal working condition. The methodologies do not address conditions of deteriorated or otherwise damaged materials of construction, nor do they address operating conditions that differ significantly from the scenarios described herein.”

The current language in Section 7.1 addresses emissions estimating methodologies for routine emissions from fixed roof tanks and floating roof tanks. These current equations were developed to estimate average annual losses for storage tanks. According to the EPA’s proposed changes, the revisions address emissions estimating methodologies for the following situations and events:

  • Landing a floating roof

  • Tank cleaning

  • Tanks containing unstable liquids or tanks storing liquids which contain gases that have the potential to flash out of solution (flashing)

  • Variable vapor space tanks

  • Pressure tanks designed as closed systems without emissions to the atmosphere

  • Time periods shorter than one year

  • Internal floating roof tanks with closed vent systems

The proposed revisions to AP-42 Section 7.1 also include the following:

  • Case-specific liquid surface temperature determination

  • Adapting equations for heating cycles in fixed roof tanks

  • Applying Raoult’s Law to calculate the contribution of individual chemical species to the total emissions

  • Proposed revisions to the equations in Section 7.1.6. These equations, used to obtain approximate values, have been replaced with updated equations that the EPA believes will be more accurate.

CFR Environmental has a long track record of providing support related to air permitting, compliance, and reporting projects for the petroleum and chemical industry, including expertise in AP-42 compliance. To guide its clients in the petroleum and chemical industries, CFR Environmental has created a software program, CFR-E, using Chapter 7.1 of AP-42 that accurately calculates air emissions from the storage of bulk organic liquids. The CFR-E software contains hundreds of chemicals and petroleum products, meterological data for any major city in North America, and can calculate VOC emissions for all major types of storage tanks. Our air expertise also includes Renewable Operating Permits (ROP), Permits to Install (PTI) and Potential to Emit (PTE) projects for compliance with state and federal regulations. Contact us to learn more about our air consulting services.

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