Flare Knockout Drum and Liquid Control

Entrained liquids in a flare stream tend to reduce combustion efficiency, often leading to increased emissions. This is why it helps to install a Flare Knock Out Drum (FKOD) upstream of a flare stack. It can help separate the liquid from gas in the system. It can also hold and store the maximum amount of fluids.

In addition to this, according to the AER Directive 060 – Upstream Petroleum Industry Flaring, Incinerating, and Venting, temporary and permanent flare systems are required to have FKOD. Read on to learn more about regulatory standards.

  • Flare Knockout Drum and Liquid Control
  • Flare Gas Recovery: Reducing and monitoring flare gas

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Directive 060 for Liquid Separation in Flare Knockout Drum

As per API Standard 521, flare knockout drum sizing must be according to the following:

  • Size of the Droplets
    An FKOD should be designed in a way that helps to remove droplets that have 300 – 600 microns or larger diameter. This is because larger droplets may cause the flare stack to produce smoke, which is highly undesirable.
  • Volume of Liquids
    The volume of liquids to be released from a pressure relief valve or an emergency shutdown should be considered when designing the separator.
  • The Capacity of Flare Knockout Drum
    The separator should be large enough to contain the release of any liquids. As a rule of thumb, it shouldn’t take up more than 20% capacity of the FKOD.
  • Gas Velocity
    The disengaging space (at 20% capacity) between the top of the liquid and the outlet of the stack must allow the gas velocity to decelerate low enough to allow the liquid droplets to fall because of gravity.
  • Visual Level Indicators
    Flare KO drums must be equipped with visual level indicators to ensure that the liquid retention in the device does not surpass the maximum level under any operating condition.
  • Alarms & Shutdowns
    The flare knock out drums must have high-level alarms or facility shutdowns to help control the liquid level.

AER Directive 55 Storage Requirements for Flare KO Drums

According to AER Directive 55 Storage Requirements, the liquids contained in an FKOD are considered as temporary storage. They do not require secondary containment. In addition to this, the accumulated fluids must be removed and disposed of at regular intervals. The rule of thumb is to remove the liquids once they reach 20% of the separator’s capacity.

We Can Help You with Flare Knockout Drum Sizing & Design

Crimtech has a wide selection of oil and gas production equipment. We have stock that is ready to be put into service. We aim to offer reliable advice and accurate solutions with regards to fabrication services, including pipefitting, welding, and instrumentation. We have the resources and expertise to understand your needs and complete a project on time. We also offer flexible rent, lease, and financing options.

If you are concerned that your flare knockout drum may be undersized, reach out to our engineering department by calling 403-342-7579 or 1-800-993-9958. Our experts will be more than happy to help you.

Request a Project Discussion: 403-342-7579 or
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