An Evaluation of Flare Combustion Efficiency Using Open-Path Fourier Transform Infrared Technology

Area of Science:

• Environmental Science
• Chemical Engineering
• Combustion Science

Background:

• Flares are crucial for destroying organic compounds and combustible materials.
• Reduced Btu content in flare gas may lower combustion efficiency, with some studies suggesting efficiencies as low as 65%.
• Existing models predict flare efficiency based on wind speed and discharge velocity.

Purpose of the Study:

• To evaluate the combustion efficiency of a low-Btu flare gas (primarily CO) using Open-path Fourier transform infrared (OP-FTIR) technology.
• To compare OP-FTIR findings with predictions from established combustion models.
• To develop and apply methods for quantifying efficiency in a dual-stack flare system.

Main Methods:

• Utilized Open-path Fourier transform infrared (OP-FTIR) technology for real-time gas analysis.
• Monitored ratios of carbon monoxide (CO) to carbon dioxide (CO2) and CO to tracer gases (SF6 and CF4).
• Employed dispersion modeling and developed a method to differentiate and quantify efficiency from two separate flare stacks.

Main Results:

• OP-FTIR measurements indicated combustion efficiencies consistently above 90% for the low-Btu flare.
• Combustion models predicted significantly lower efficiencies, some as low as 30%.
• A novel method successfully distinguished between two flare stacks and quantified individual efficiencies.

Conclusions:

• OP-FTIR is a reliable technology for accurately assessing flare combustion efficiency, even for low-Btu gases.
• Current combustion models may overestimate the negative impact of low Btu content and specific operating conditions on flare efficiency.
• The developed methodology allows for precise efficiency determination in complex, multi-stack flare environments.