New approach to reduce flaring emissions in production wells
By Dr. Neil Canter, Contributing Editor | TLT Tech Beat August 2025
A study has been published to assess the ability of different flare designs to effectively combust methane.
HIGHLIGHTS
Flaring of natural gas is done to relieve pressure in pipelines and ensure pressure does not accumulate in refineries or production wells.
A study has been conducted to better understand the performance of non-assisted flaring in an effort to reduce emitting methane, a potent greenhouse gas.
An indoor calorimeter measured destruction removal efficiency and combustion efficiency for natural gas and propane using a number of experimental parameters.
Testing the effects of crosswind moving across the flare showed that destruction removal efficiency was particularly effective at low flare gas flow rates.
When many of us visit or travel past a refinery, or gas production site, one of the lasting images is that of a flame at the top of a stack. The flame is produced by a controlled process known as flaring (see Figure 1).
Jenna Stolzman, a doctoral graduate student in the mechanical engineering department at The University of Michigan in Ann Arbor, Mich., says, “Flaring is conducted as a safe way to relieve pressure in pipelines and to ensure pressure does not accumulate. Operators also use flaring when gas is not economical or cost effective to recover.”
Figure 1. Researchers developed and tested an advanced methane flare burner using additive manufacturing and machine learning. A new study found that the new design eliminated 98% of methane vented during oil production. Figure courtesy of Southwest Research Institute.
The main component in natural gas is methane which is a potent greenhouse gas that has 28 times the global warming potential of carbon dioxide and is 84 times more potent over a 20-year time scale. Ms. Alex Schluneker, principal engineer at Southwest Research Institute in San Antonio, Texas, says, “At a methane mitigation summit in 2024, the attendees indicated that routine flaring is way down as users are only burning methane when necessary. They flare methane to make sure this flammable gas is not dumped into the atmosphere.”
One cause for concern with flaring is that recent studies found that destruction efficiency may be lower at sites in the U.S. than what is assumed by the U.S. government. Destruction efficiency represents the percentage of hydrocarbons entering the flare system that are destroyed via combustion.
Stolzman says, “U.S. industry and the federal government assume that flares meet a destruction efficiency of 98% as long as they follow the code of regulations which has specifications such as minimum heating values and maximum exit velocities. Some recent studies have shown this level of destruction efficiency has not been met. In particular, airborne sampling studies in the main oil and gas regions of the U.S. found the average destruction efficiency was approximately 91%, which is 7% lower than that assumed by the U.S. Environmental Protection Agency (EPA). This means that methane emissions can be up to five times higher than what EPA estimates for their inventories.”
Facilities use different types of flares such as steam-assist, air-assist and non-assist technologies. Stolzman explains, “Steam or air can be injected into the flare to assist with combustion. These types of flares are more commonly used at refineries in places where either or both are available. This capability is commonly used in refineries or in places where steam, air and access to power for a blower/fan are available. But there are remote sites such as production wells where access to power, steam and air is limited. In these cases, non-assisted flaring is used, which may involve low-pressure, low flare gas flow rates and a basic pipe or utility flare.”
Stolzman, Schluneker and their colleagues realized that low-flow non-assisted flares might be inefficient in destroying methane and there was need to better understand the performance of low-flow non-assisted flares under a more controlled environment.
A study has now been published to better understand the performance of non-assisted flares in a new indoor testing facility and to assess the ability of different flare designs to effectively combust methane.
Crosswind
The experimental setup for this study involved the use of an indoor calorimeter that can operate under a controlled environment. Schluneker says,” Our facility contained an exhaust hood that is 6 meters by 6 meters in cross section and is situated 7.6 meters above the ground. This hood was used to collect the entire plume from the flare under different operating conditions. Gas sampling was conducted from an exhaust duct about 6 meters from the top of the hood and approximately 15 meters from the exit of the flare pipe. This represents the unique aspect of our setup where we can evaluate the performance of the flare by sampling the gases in the exhaust and determine the composition of the gases resulting from combustion.”
The researchers determined the destruction removal efficiency and combustion efficiency for each experiment. Stolzman says, “Combustion efficiency is a measure of how much of the flare gas is converted to carbon dioxide and water. In effect, it is measured by taking the ratio of carbon dioxide to total carbon in the plume.”
Carbon dioxide and carbon monoxide were analyzed using single-beam single-wavelength infrared absorption spectroscopy and hydrocarbons were evaluated by gas chromatography. A baseline flare-tip geometry that contained a 7.5 centimeter-schedule -40 pipe was used as the control along with two alternative designs.
Natural gas and propane were each used as the gas in the controlled testing. Experimental parameters used in the study included the lower heating value (determined via flare gas composition), flare gas flow rate and exit Reynolds number. Stolzman says, “It is very challenging to design a flare tip without air or steam assist that can work with both natural gas and propane. The latter tends to smoke more, which is against EPA requirements.”
A fourth parameter investigated was the crosswind moving across the flare. Stolzman says, “We found in this study that crosswinds blowing in a perpendicular orientation to the flare can have a significant effect on destruction removal efficiency particularly at low flare gas flow rates. We also found higher flare gas flow rates were more resistant to crosswind effects.”
Initial results revealed that at low crosswind conditions, combustion efficiency was greater than 98% for all operating conditions and for each of the three flare-tip geometry designs tested. The baseline design displayed lower combustion efficiency (<96.5%) for natural gas at higher wind speeds and lower flare gas flow rates. The two experimental designs exhibited significantly improved performance compared to the baseline.
Stolzman says, “Our work continues in developing and evaluating new flare designs that are more cost effective and efficient. As part of this process, we are doing non-reacting and reacting flow modeling and will continue to evaluate designs at the indoor calorimeter.”
Additional information can be found in a recent article1 or by contacting Joanna Quintanilla, lead communications specialist at Southwest Research Institute, at joanna.quintanilla@swri.org.
REFERENCES
1. Stolzman, J., Gutierrez, L, Schluneker, A. and Woolridge, M. (2025), “An experimental study on the effects of waste-gas composition and crosswind on non-assisted flares using a novel indoor testing approach,” Industrial & Engineering Chemistry Research, 64 (2), pp. 967-980.
Neil Canter heads his own consulting company, Chemical Solutions, in Willow Grove, Pa. Ideas for Tech Beat can be submitted to him at neilcanter@comcast.net