What is a Flare Stack?


A flare stack refers to an elevated vertical stack used for burning off unusable waste gas in a variety of oil and gas production applications. Waste gases are either uneconomical to recover/retain, or released during planned or unplanned over-pressuring of plant equipment. Waste gases are released to the flare via piping (flare header) and burned as they exit the flare stack.

Flare Systems

What makes a Flare Stack properly designed?

1. To maintain a stable flame during operation. An unstable flame can either blow-off or ingress back into the flare tip;
2. To ensure the flame is high enough to limit operators’ ground-level exposure to thermal radiation, emissions or noise;
3. To comply with all the requirements from the customer’s and regional regulatory bodies.

The standard Tornado Technologies Flare complies with the following Standards/Guidelines where applicable:

  • Flare Design Guidelines
    • API 521
    • API 537
  • Construction Guidelines
    • ASME B31.1
    • API 537
  • Environmental Regulations
    • 40CFR60
    • AEUB Directive 060
  • Structural Standards
    • ANSI/ASC 7-88, &-97 & 7-98
    • NBC Canadian

What are the primary Flare Design Parameters?

 Overall flare height and internal tip diameters (the main construction considerations) are directly affected by the following design parameters:

Radiation Limits

Ground Level Concentration Limits

Noise Limits

Structural stability

Chemical Composition of Waste Gas

Environmental Conditions

Allowable Pressure Drop

Exit Velocity of Waste Gas


How do I choose the right Flare?

To fully understand your application, the following questions should be considered:

1. What is the flow rate of the gas that is to be combusted?

2. Will this flow be present at all times?

3. What are the utilities present onsite?

4. Does the flare need to be smokeless?

5. How combustible is the gas that is to be flared?

6. Is the gas to be flared dangerous (acidic or toxic)?

7. Will the gas composition smoke?

8. What are the regulations that need to be adhered to in the flare’s design?


Types of Flares

There are two general families of flare systems that Tornado works with: Utility Flares and Engineered Smokeless Flares.

Utility Flares

A Utility (non-assisted) flare is the most basic type of flare. The flare’s height is calculated based on the radiation and dispersion flaring emissions at the ground that are caused by the combustion process.

A utility flare tip’s internal diameter is sized based on:



The exit velocity of the flare, and

The allowable pressure drop

Engineered Smokeless Flares

Tornado has developed a broad range of assisted flares specifically designed to meet a large spectrum of gas compositions and varied operating conditions. Waste gases burn cleanly and without visible black smoke to meet the most stringent regulations. All designs are driven by flare performance and operating costs. Assisted tips can even be retrofitted onto existing flares cost effectively.

Air-Assist Flares

Air Assisted Smokeless Combustion exists where air is added to the Waste Gas Stream at the tip of the Flare stack to eliminate smoking.

There are two different Air Assist Flare Types typically provided by Tornado:

1. Retrofit Air Assisted Flare

This type of air assisted flare is where Tornado takes an existing Utility Flare that is smoking and provides an external air duct, tip and blower to convert it to a smokeless air assisted flare.

1. New Air Assisted Flare

Flame Assist Off  Flame Assist On

This type of application is where either Tornado or you have determined that the waste stream will smoke and that an air assisted flare is the best choice to prevent the stream from smoking during flaring. This design has less thermal stress, and is more aesthetically pleasing than a retrofit design mentioned above and as such is used on most new air assist flare projects.

High Pressure Gas-Assist Flares

The general principle behind gas-assisted flares is to introduce a high pressure gas to the waste steam just after exiting the flare tip to eliminate smoking. The addition of gas will increase the radiation produced by the flare, which may in turn add to the overall flare’s required height to compensate. Let Tornado Technologies assist you with determining if gas assisted or air assisted flaring is the best choice to eliminate or prevent a smoking flare.

Steam Assist Flares

The general principle behind steam-assisted flares is to introduce high pressure steam to the waste gas steam just after exiting the flare tip.

Low- Pressure Gas- Assist

A low pressure gas assist maybe required when flaring acid/toxic gases with low heating values. The ring burner creates a flame curtain between the tip of the flare and the ignition point of the flare’s flame front to ensure that any reactants do not escape without first hitting a flame. Thus 100% of the gas exiting the flare is given the required energy to combust.

Sonic Flares

Sonic flares are used when the waste gas volumes to be flared are of an extreme level. A sonic flare creates the most noise, longest flame length, highest pressures, and most radiation. They should only be considered when there is no concern about noise, radiation or flame length.

PDF SPEC - Flare Stacks