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Recent EU climate policies and international reporting standards, including OGMP 2.0, have imposed stringent requirements on methane emissions from the oil and gas sector. Due to its high global warming potential, methane has become a major regulatory target, with industrial flares used for waste gas disposal required to achieve at least 99% methane destruction efficiency. These requirements aim to reduce the release of unburned hydrocarbons and support the transition from estimated emission factors to direct field measurements.
This work presents experimental results obtained on a mobile Esders degassing flare with a maximum gas flow rate of 209 m³/h operating under purely diffusive combustion conditions. Two complementary techniques were applied to quantify methane destruction: direct gas sampling with a Flame Ionization Detector (FID) and passive Fourier-Transform Infrared spectroscopy (pFTIR). The former requires physical access to the combustion plume and careful positioning of the sampling probe to avoid secondary oxidation and excessive dilution by ambient air. The latter enables remote acquisition of absorption–emission spectra from a distance of approximately 30 m, yielding column concentrations in ppm·m.
In the contact method, unburned methane was quantified using the equation:
$ E_{\mathrm{CH_4}} = OGC_{\mathrm{wet}} \cdot \frac{21}{21 - O_2} \cdot V_{\mathrm{wet}} \cdot \frac{M_{\mathrm{CH_4}}}{M_{\mathrm{C}}} $
where OGC denotes the organic carbon content in the exhaust gas, O2 represents oxygen content, and the remaining terms account for dilution correction and carbon-to-methane conversion. Experimental data showed that 6.531 g of methane remained unburned out of 716.1 g supplied, corresponding to a destruction efficiency of 99.09%.
In the pFTIR method, methane destruction was evaluated using the carbon balance:
$ DE = 100 \cdot \frac{CO_2 + CO}{CO_2 + CO + THC_w} $
where total hydrocarbons in the denominator represent unburned fuel fractions. Analysis of 52 independent spectra resulted in an average destruction efficiency of 99.77%, while radial calculations yielded 99.75%, indicating excellent repeatability. As pFTIR does not require physical contact with the flame, it avoids issues associated with turbulence, condensation in sampling lines, or analyzer power supply, although it remains sensitive to atmospheric conditions such as humidity or precipitation.
Both methods yielded efficiencies above 99%, confirming compliance of the tested flare with EU and OGMP 2.0 requirements. The difference of only 0.66 percentage points between the lowest and highest value demonstrates consistency between the approaches. These results indicate that remote optical techniques, owing to their universality and operational safety, have strong potential to become preferred tools for field-based reporting of flare combustion performance, supporting the transition from literature-based estimates to true measurement-based quantification.
