Retrofitting Air-Assisted Flares to Attain 99.5% Destruction Efficiency
Cimarron’s senior technical staff gave presentations for the 2022 Onshore Wellsite Facilities Conference held in Houston, TX on September 20-22, 2022. One presentation was regarding high destruction and removal efficiency (DRE) flares which included valuable technical information for the design, sizing, operation, and monitoring of air-assisted flares to attain 99.5% destruction efficiency.
This informative talk (about 30 minutes) is worth your time if you deal with flares in your work. You can view the talk on YouTube at: High DRE Flares – Evaluating new technologies to reduce flare emissions by an additional 75%: YouTubeLink
Below is a summary and key information from the presentation.
In the talk, Mr. Robert Webb discusses general flaring design and the use, design features and components for air-assisted flares. Videos examples of over-aeration, under-aeration and Stoichiometric-combustion are shown. Also, the video explains how the color of the flare flame relates to DRE. The latter part of the video discusses Cimarron’s new DreamDuoTM flares that can combust methane at >99.5% DRE.
The term DRE stands for Destruction and Removal Efficiency. For flares, this is basically the conversion efficiency of natural gas to the main combustion product of CO2 and water vapor.
For typical open-tipped flare, most environmental regulatory agencies accept a DRE of 98% without testing. Most regulations (Federal NSPS OOOO/OOOOa, Colorado Reg 7) require a minimum control efficiency of 95%.
Flares designed to meet 40CFR 60.18 are typically allowed to use a 98% DRE for oil and gas emission inventories and for oil and gas air permit application emission calculations.
Stoichiometry of Flaring
The word stoichiometry derives from ancient Greek words, “Stoicheion” meaning ingredient and “metron” meaning measuring.
The simplified combustion of methane (CH4) is shown below:
Byproducts when using air as the oxygen source include:
𝑆𝑂𝑥 Results from combustion of sulfur compounds
𝑁𝑂𝑥 Forms from high temperature reaction of nitrogen and oxygen
𝐶𝑂 Byproduct of poor combustion process, can be minimized with proper burner design
The stoichiometric ratio is the ideal air to fuel ratio where there is just enough oxygen to burn all fuel without any excess left over.
Smokeless Flare Operations
All flare applications should operate smokeless. The typical measurement for smoke is the Ringelmann Scale. Observers that are properly trained use EPA Method 9 to assess the amount of smoking based the Ringelmann Scale.
Proper design and operating parameters are needed to eliminate smoke. Consideration for flare applications include:
- Combusting Paraffins, Olefins, Diolefins, Acetylenes, Aromatics can lead to smoke.
- Combusting Methane, Hydrogen, Carbon Monoxide, Ammonia, Hydrogen Sulfide do not smoke.
- The calculated amount of OXYGEN (air) must be available in the combustion zone at the beginning of the combustion process.
- Carbon to Hydrogen C/H ratio < 0.25 conservatively promotes “smokeless” flaring.
- Carbon to Hydrogen C/H ratio > 0.28 tends to “smoke.”
- Lower Heating Value <1000 Btu/ft3 promotes “smokeless” flaring.
- Gas Molecular Weight MW <20 promotes “smokeless” flaring.
To eliminate smoke, the flare system needs to ensure that enough air (oxygen) is available at the beginning of the combustion process and is well mixed with the waste vapor. This can be accomplished using the following technologies:
- Pressure Assist Flare where high pressure waste gas is available (greater than 20 psig)
- Air Assist Flares that use an electric powered blower
- Gas Assist Flares using natural gas injection
- Enhanced Tip Design that creates greater Air/Fuel boundary
As discussed in the talk, experience has shown that the highest DRE is right at incipient point of smoke formation in the flame. Under-aeration and over-aeration both result in unburned waste gas emissions.
Flame color correlates with DRE and smoke formation. A flame color of a mix of pink and orange with small amounts of marbling (internal smoke) yields an optimal DRE. Clear or pale blue flames can indicate DRE’s less than 98%.
New DreamDuoTM Combination of Variable Mach & Air-Assisted Flare and DRE-MaxTM
Cimarron was selected by the Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) (code name REMEDY) to receive a grant to design an Advance Control System to use with a hybrid flare design to ensure >99.5% destruction efficiency. The flare handles both high and low-pressure gas streams. The result of this work was Cimarron’s DreamDuoTM, This flare is designed using a combination Variable Mach & Air-Assisted Flare that yields a 99% destruction of methane. While using the Patent Pending DRE-MaxTM Advanced Control System to control the DreamDuoTM, the system was able to consistently achieve >99.5 DRE.
Cimarron’s DreamDuoTM flare maximizes DRE by using a variable frequency drive blower along with a monitoring and the DRE-MaxTM control system.
Below are results of ARPA-E testing for the DreamDuoTM flare that demonstrated a DRE greater than 99.5% for a natural gas stream. The DRE testing used a Passive Fourier Transform Infrared (PFTIR) analyzer.
|Time||Test #||Efficiency (%)|
|Start Time||End Time||Test Desc.||DRE Avg||Notes|
|1:09 PM||1:14 PM||Test 1||99.6%||60 MSCFD LP only|
|1.23 PM||1:27 PM||Test 2||99.7%||1500 MSCFD HP only|
|1:28 PM||1:31 PM||Test 3||99.7%||1500 MSCFD HP only|
|1:34 PM||1:37 PM||Test 4||99.6%||5000 MSCFD HP only|
|1:41 PM||1:46 PM||Test 5||99.9%||1100 MSCFD HP only|
|1:49 PM||1:53 PM||Test 6||100.0%||500 MSCFD HP only|
|1:58 PM||2:02 PM||Test 7||99.9%||220 MSCFD HP only|
|2:09 PM||2:13 PM||Test 8||100.0%||330 MSCFD HP only|
Summary and Conclusions
The term DRE stands for destruction and removal efficiency. For flares burning natural gas, this is basically the conversion efficiency of natural gas to the main combustion product of CO2 and water.
Cimarron’s DreamDuoTM flare achieves DREs greater than 99.5% by using a variable frequency drive blower along with a DRE-MaxTM control system. Testing under an ARPA-E grant program used a Passive Fourier Transform Infrared (PFTIR) analyzer to demonstrate the high DRE.
The typical, accepted regulatory default DRE for flares combusting natural gas is 98%. An increase in a flare DRE from 98% to 99.5% yields a 75% reduction in emissions (2% venting reduced down to 0.5% venting). This higher DRE would reduce significantly reported methane flaring emissions and could potentially reduce future methane fees by 75% for oil and gas operations.
Cimarron – Who We Are
Cimarron’s vision is to work with our clients to create a cleaner environment.
The company engineers and manufactures environmental, production and process equipment for the upstream, midstream and downstream energy industries, as well as environmental control solutions for biogas at wastewater facilities, digester tanks and landfills.
Cimarron offers our customers the know-how and environmental expertise to meet the environmental standards of today and tomorrow. Cimarron is committed to bring value to the Energy industry and their shareholders based on our financial strength, experienced personnel, and engineering capabilities.
As a company, we thrive every day to make a difference through innovation (e.g. ESG), customer focus, and operational efficiency. In addition to being present in all major regions in the US, Cimarron serves more than 45 countries around the world, ranging from offshore to desert. From key operational centers in the United States, Italy and the United Arab Emirates, Cimarron offers ongoing service and support through its own field service personnel and strategic third-party partners, creating a cleaner environment for our customers and their shareholders.
Since its founding in the mid-1970’s in Oklahoma, the company’s product offering has expanded from production equipment to include the largest line of environmental solutions that capture or incinerate fugitive vapors. With the acquisitions of HY-BON/EDI in 2019 and AEREON (including Jordan Technologies) in 2020, Cimarron has added strong brands, products, and services to its portfolio.