Measurement of unburned methane in air-assisted flares using FTIR absorption spectroscopy on extracted gases

This work presents an experimental methodology for the quantification of unburned methane (CH 4 ) flow in laboratory-scale air assisted flares. The approach relies on the use of a mid-infrared hyperspectral Fourier Transform Infrared (FTIR) imaging system operated in absorption mode, in combination with a gas capture setup that ensures complete extraction of combustion products. The extracted gases are directed through a T-shaped tube with an extended optical path, where their transmittance spectra are recorded and fitted to a radiative transfer model to retrieve CH 4 column densities. The core of the method is a calibration procedure that establishes a relationship between these column densities and mass flow rates by releasing known CH 4 flows through the burner and measuring the corresponding column densities in the tube. The methodology is applied to assess the performance in terms of the CH 4 destruction and removal efficiency (DRE CH 4 ) of a flare under different levels of air assistance and crosswind. The results reveal a critical threshold beyond which CH 4 emissions increase significantly due to partial flame extinction, thus lowering the DRE CH 4 , and demonstrate the method’s ability to resolve temporal variations in combustion efficiency with a time resolution of 10 s. Although developed in a controlled laboratory setting, the proposed technique provides a reliable framework for studying combustion instability and validating field-deployable remote sensing technologies. Its implementation can contribute to improving flare performance assessment and to the mitigation of methane emissions from industrial combustion sources.