Flaring in the oil and gas industry has been around since companies started to drill for oil. Flaring was used to relieve pressure from the wells or eliminate harmful casing gas that would otherwise vent. In addition, when well gas is not economical to transfer or capture, waste gases are flared as a form of safety. This practice was developed in the 1930s and is still, in many locations, a practice utilized today.
Since flaring was first used, it has been shown to be a fairly effective tool for the reduction of waste gas venting on oil and gas sites, especially in emergency applications. Having said that, there are now other solutions that can be more effective and affordable.
One should know several things when considering flares for an application.
- Types of Flares
- Combustion Efficiencies
- Spacing Restrictions
- Ground Radiant Heat
- Light Pollution
- Unintented Venting
- Other Technologies
Types of Flare
Several types of flares have been developed over the years.
- Single point flares
- Multi-point flares
- Steam or air assisted flares
- Ground flares / flare pits
The most common flares in use today are elevated single or multi-point flares.
Flaring Combustion Efficiency
By the nature of design, the flame of a flare is open to the atmosphere, including wind, rain & snow. These elements will impact the quality of the flame and, in turn, the combustion efficiency. Other parameters, such as the quality of gas or amount of steam (if steam-assisted) can also impact the combustion efficiency.
According to a study completed by the EPA (EPA, 2012), a good flare performance has 96.5% Combustion Efficiency. However, other studies show that many factors can influence this combustion performance. For example, Blackwood, suggested that lower BTU flares can have efficiencies as low as 65% (Blackwood, 2000). Makeup fuel is typically used to increase the BTU value in these situations.
Also, because there is no combustion chamber on a flare, the combustion environment cannot be controlled, resulting in a wide range of combustion efficiencies.
Photos showing flaring 1) clean combustion (good gas, no wind) vs 2) poor combustion efficiency (low-quality gas, wind).
Combustion Efficiency vs Destruction Efficiency
Destruction efficiency is a measure of how much hydrocarbon is destroyed, and combustion efficiency is a measure of how much hydrocarbon was converted to CO2 and H2O (Baukal, 2001).
By definition, the destruction efficiency will always be greater than or equal to the combustion efficiency. Baukal estimated that a 1.5% difference is a reasonable estimation on average. For example, a flare with a destruction efficiency of 98% may only have a combustion efficiency of 96.5%.
Assuming a waste gas stream consisting of 100% CH4, we could expect the combustion reaction to produce Carbon Dioxide and Water. However, this does not consider any of the variables (i.e. contaminants in the waste gas, weather events, etc.) which could affect the conversion percentage (Combustion Efficiency).
Like Saskatchewan, Canada, some jurisdictions will allow for better emissions factors when calculating for enclosed combustors vs flares. This factor helps producers become more compliant with local emissions requirements or save money from administrative fees.
Spacing Restrictions
Spacing for flares is typically 50 meters from the well, tanks or process equipment (Alberta Directive 60). There are exceptions in some areas where spacing has been relaxed. For example, Cold Heavy Oil Production (CHOPS) is only 25m.
Incinerators typically mirror the spacing requirements of a flare. Enclosed Combustors on the other hand are designed with several safety features which allow them to be spaced at 10-meters in many jurisdictions.
Ground Radiant Heat
The heat generated from a flare is referred to as Thermal Radiation and is a consideration in flare design. This calculation is used to establish flare stack heights and setbacks to keep workers and equipment safe. A flare must not exceed 4.73 kilowatts per square meter (kW/m2)
In Canada, thermal radiation from a flare can significantly impact the ground melt. This influences the ground around the flare and can cause the ground to become soft and unstable in winter conditions when the ground would otherwise be frozen. The soft ground can be difficult to maneuver over and trucks can get stuck in these areas.
Light Pollution
A running flare will produce constant visible light. Although many sites are located in areas without neighbours or residents nearby, many are not. This light pollution is very noticeable at night and can cause nearby residents discomfort.
To give an idea of the level of light pollution produced, check out the below photo of the USA at night. The light produced from flaring in the Bakken rivals some large cities on the east coast.
Photo Reference: https://www.npr.org/sections/krulwich/2013/01/16/169511949/a-mysterious-patch-of-light-shows-up-in-the-north-dakota-dark
Unintended Venting
Unlit flares are a significant source of methane venting and are typically caused by malfunctioning of the flare. In the Permian, producers failed to light about 5% of their flares, resulting in methane being released into the atmosphere (www.spglobal.com). Newer flaring technologies reduce this risk; however, flaring has been around for a long time, and older equipment and designs are still available and being used. Policies and company procedures must align to ensure that operational practices on flare maintenance don’t lapse, causing flares to malfunction or remain unlit for extended periods (bakthavachsakam, 2018)
Other Technologies?
Enclosed Combustors and Incinerators have been specifically developed as an alternative to flaring.
Because Enclosed Combustors have been purposely designed to solve the challenges associated with flaring, they have several key benefits.
- No visible flame
- The combustion environment is controlled allowing for improved combustion efficiencies
- Close spacing eligible
- BMS systems prevent unintended venting
- Very little radiant heat (Some Manufacturer Designs)
The one benefit that flares used to have over enclosed combustors was price, but over the last decade, enclosed combustors have become more affordable, even rivalling flares. This affordability, combined with the other benefits listed above, makes combustors attractive over the traditional flaring setup.
EnviroVault & Emission RX has focused on providing our clients with long-lasting, reliable and affordable waste gas combustors & incinerators for large and small projects.
References
EPA, 2012, Parameters for Properly Designed and Operated Flares
Thomas R. Blackwood (2000) An Evaluation of Flare Combustion Efficiency Using Open-Path Fourier Transform Infrared Technology, Journal of the Air & Waste Management Association,
Bakthavachsalam, V. et al. (2018), Maintaining flare tip health, Society of Petroleum Engineers, presentation at International Petroleum Exhibition and Conference, Abu Dhabi
https://www.npr.org/sections/krulwich/2013/01/16/169511949/a-mysterious-patch-of-light-shows-up-in-the-north-dakota-dark