Air Quality Division Tank Degassing and Cleaning Rules; TSH :May 15, 2008 Page 1 Changes to Tank...

Air Quality Division • Tank Degassing and Cleaning Rules; TSH :May 15, 2008 •

Changes to Tank Degassing and Cleaning Rules

Texas Association of Environmental Professionals

Air Quality Division • Teresa Hurley, P.E. • May 15, 2008


Tank Degassing and Cleaning Rules

• What are the current requirements?

• Why were the rules changed?

• What changed?

• When do changes take effect?

• Questions


What are the current requirements?

• 30 TAC Chapter 115 Subchapter F Division 3: Degassing or Cleaning of Stationary, Marine, or Transport Vessels

• Applicability:– Stationary tanks with capacity ≥ one million gallons

– Transport vessels with capacity ≥ 8,000 gallons

– Marine vessels with capacity ≥ 420,000 gallons

– Vapor space partial pressure ≥ 0.5 psia



• Control Requirements:– 90% control of vapors

– No avoidable leaks

– Must use vapor-tight connections

– No intentional bypass of vapor control device



• Vapors must be routed to control device until:– Partial vapor pressure < 0.5 psia; 19,000 ppm by weight;

34,000 ppm by volume as methane;

OR– Turnover of at least four vapor space volumes has

occurred

• Vapors can be vented to the atmosphere after any of the above conditions is satisfied


Why were the rules changed?

• Studies have indicated that VOC emissions in HGB area are under-reported in emissions inventories.

• Remote sensing study results have indicated that degassing emissions are under-reported.

• Rule changes were made to reduce the previously under-reported emissions.


What changed?

• Eliminated “four turnover” condition for allowing vent to atmosphere– Confusion over measurement: must be volume passing

through tank vapor space; not measured after combustion control

– Does not account for presence of residual liquid in the tank


Floating Roof Tank - Drain Dry

Source: API, 2004


Floating Roof Tank with a Liquid Heel

Source: API, 2004


What changed?

• Control degassing vapors until

– VOC concentration of vapors ≤ 34,000 ppmv as methane, or

– < 50% of lower explosive limit


What changed?

• Monitor VOC concentration of degassing vapors according to 115.545(11)– Allow flexibility in monitoring methods– Maintain records to demonstrate that method works for

compounds present


What changed?

• Specified monitoring methods:– Test Method 21 (40 CFR Part 60, Appendix A)– Test Method 18 (40 CFR Part 60, Appendix A)– Bag samples – Test Method 25A (40 CFR Part 60, Appendix A) – Portable hydrocarbon gas analyzer using appropriate

detector– Lower explosive limit detector calibrated and

maintained according to manufacturer's specifications


What changed?

• Monitoring must continue while vapors are vented to atmosphere:– At least once every 12 hours if ventilation is continuous– If ventilation ceases for more than 4 hours,

concentration must be rechecked before venting to atmosphere

– Monitoring can be discontinued after five consecutive readings less than 34,000 ppmv or 50% of LEL


What changed?

• Require control of vapors for smaller tanks:– Capacity ≥ 250,000 with vapor pressure ≥ 0.5 psia – Capacity ≥ 75,000 with vapor pressure > 2.6 psia


When do changes take effect?

• Compliance date for new requirements is January 1, 2009


For more information

Teresa S. Hurley, P.E.

TCEQ Air Quality Planning Section

512-239-5316

[email protected]

Air Quality Division Tank Degassing and Cleaning Rules; TSH :May 15, 2008 Page 1 Changes to Tank...

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