An evaluation of flare combustion efficiency using open-path Fourier transform infrared technology

Open-path Fourier transform infrared (OP-FTIR) technology was used to evaluate the combustion efficiency of a flare for comparison to several combustion models. Most flares have been considered an effective method for destroying organic compounds and anything that burns. As the Btu content of the flare gas is reduced, the combustion efficiency may also be reduced. Recent studies have suggested that lower Btu flares may have efficiencies as low as 65%. In addition, models have been developed to predict the effect of wind speed and stack discharge velocity on the combustion efficiency. This study was conducted on a low-Btu flare gas that is primarily CO. While the models would predict efficiencies as low as 30%, the sampling using OP-FTIR showed most combustion efficiencies well above 90%. Three methods were used to track combustion efficiency: monitoring the ratio of CO to CO2, monitoring the ratio of CO to tracer gas, and dispersion modeling. This study was complicated by the presence of two flare stacks, thus two tracer gases were used-SF6 and CF4. A method was developed for distinguishing between the two stacks and quantifying the efficiency in each stack.