Air permits for oil and gas (O&G) production facilities include Federal EPA and State requirements for storage tanks for crude oil, condensate and produced water. The main EPA rules applying to O&G storage tanks are the New Source Performance Standards (NSPS) OOOO and OOOOa. Individual state environmental regulatory agencies may have their own storage tank regulations that might also apply.

Below are some guidance tips that will help ensure your storage tank facilities stay in compliance.


Tip 1: Ensure that the thief/gauging hatches are in good condition and sealing properly.

This includes ensuring that the seals are made of a material that is compatible with the oil or produced water stored and that the hatch used is designed to maintain the necessary amount positive pressure in the tank.

This is especially important for storage tanks that are routed to an emissions control device (VRU, flare, enclosed combustion device – ECD). If the hatches are leaking, then a portion of the emissions are not being controlled.

Some considerations for this include:

  • Leaking hatches can be caused by over pressuring of storage tanks because of undersized piping (too small diameter) connected to a flare or vapor combustion unit.
  • Use a vapor recovery tower (VRT) to reduce the amount of flash gas liberated in the storage tanks and help ensure hatches can continuously maintain a good seal.
  • Use vapor recovery units (VRU) to collect vent gas from storage tanks and eliminate the emission from venting or flaring.


Tip 2 Optimize size of piping used to route tank vapors to the emission control device.

Optimize piping for minimum and maximum flowrate of vent gas expected so that the emission control system can handle the expected flowrates.

Use our IQR direct measurement services or a process flow simulation model to determine expected instantaneous and average vent gas flowrates. This data can be used to determine the appropriate piping diameter to use and to size the emission control device.


Tip 3. Reduce pressure drop between separator or heater treater dumping to storage tanks.

Use the lowest separator/heater treater pressure possible based on needed operating conditions.

Lowing the separator/heater treater operating pressure will only reduce emissions if flash gas from the separator/heater treater is recovered (e.g. routed to site low pressure system or to a VRU).

Another option is to use a vapor recovery tower (VRT) to reduce the amount of flash gas liberated in the storage tanks and help ensure hatches can continuously maintain a good seal. In this system, the VRT is installed and operated between the separator/heater treater and the storage tank. The VRT then operates as a low pressure separator (operating at 2 to 10 psig) that recovers the majority of the flash gas (that would have been liberated in the storage tank). The lower pressure oil from the VRT is then sent to the storage tanks. This makes it easier to keep hatches working properly.  In some cases, the use of a VRT helps a storage tank meet NSPS OOOOa and/or State emission limits and not need emission controls.

Typically, the VRT flash gas would be routed to a VRU for recovery or could be routed to a flare or VCU.


Tip 4. Optimize the pressure relief valve (PRV)

Use a pressure relief valve (PRV) that is installed and maintained as a proper functioning emergency relief valve that provides for safe storage tank operations. PRVs should not be used as process vents for routing venting during normal operations.

PRV set points for opening should be set low enough to protect storage tank structural integrity and avoid over pressuring the storage tank. Also, the set point should be high enough to exceed storage tank operating pressures during normal operations. This includes flash gas liberated during separator dump events.

For more detailed discussion on the topic go to link: EPA Compliance Alert


Cimarron’s IQR Services

Let Cimarron assist your company Identify, Quantify and Rectify (IQR) your facility emissions.  Using our IQR services your company can stay in compliance with NSPS OOOOa and state air permits and make your company money.  Our vapor recovery units (VRU), Vapor Recovery Towers (VRT) and vapor combustors units (VCU) can help you comply with storage tank emission control requirements.

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