AP-42 Chapter 7, Storage Tanks Emission Calculation Revisions
December 1, 2019

In November 2019, the EPA finalized revisions to emission calculation methods used for organic liquid storage tanks found in AP 42 Chapter 7, Section 7.1. These methods were developed by the American Petroleum Institute (API) for fixed roof and floating roof tanks. The previous revisions were made in November 2006.

Some highlights of the changes involve:

General

  • Revises calculation methods (equations, coefficients, etc.) for standing and working losses for fixed roof tanks. Only minor changes to fixed roof storage tanks calculation methods.
  • Includes calculation methods (equations, coefficients, etc.) for standing and working (withdrawal) losses for internal and external floating roof tanks.  Major changes to floating roof tank calculation methods.
  • The website contains the revised Section 7.1 along with supporting information for the revisions including (see Final Revisions to AP-42 Chapter 7, Section 7.1)
    • Final Chapter 7, Section 7.1
    • Public comments
    • Proposed revisions summary
    • Proposed revised document with redline line strikeout version

 Crude Oil Storage Tanks 14838167_s.jpg

TANKS4 Software

  • This revision will make the TANKS4 software program obsolete since EPA is not updating the TANKS4 program. The TANKS4 only calculates standing and working losses; no flashing losses are included in TANKS4.

 

State Environmental Regulators

  • The TCEQ is requiring the revised Chapter 7 methods to be used in air permit applications effective December 16, 2019.
  • Other state regulators can be expected to also require the use of the revised Chapter 7 methods.

 

Flashing Losses

  • Section 7.1.3.5 gives recommendations for estimating flashing losses from fixed roof storage tanks.
  • No equations or specific methods are discussed to quantify flashing losses.
  • Methods used to quantify flashing losses should be representative of the production from the site.

 

Typical methods used by operators to estimate flashing losses include:

  1. Direct measurement of the vent gas flowrate from the tank along with a chemical analysis of a sample of the vent gas. The measures consist in standing, working and flashing losses.
  2. Pressurized oil sample collected from the vessel (low pressure, heater treater) upstream of the tank and chemically analyzed by a lab. The lab will determine gas to oil ratio of the flash gas for the tank and chemically analyze flash gas liberated. This only estimate flashing losses - not standing and working losses.
  3. Pressurized oil sample collected from the vessel (low pressure, heater treater) upstream of the tank and is chemically analyzed in lab. Data from the pressurized oil sample is used as inputs into a process simulator (e.g., PROMax) to estimate flashing losses. Process simulators can estimate standing, working and flashing losses.

 

Concerned About Venting of Natural Gas?

Cimarron’s acquisition of HY-BON/EDI in July 2019 means that our environmental product and services offered to our oil and gas customers are further strengthened. This includes the following:

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  • Leak Detection and Repair (LDAR) services
  • Vent gas measurement services
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  • Parts

For more information on our products and services, you can contact us at +1 (844) 746-1676 or visit https://www.cimarron.com.