Viability of video imaging spectro-radiometry (VISR) for quantifying flare combustion efficiency

Video imaging spectro-radiometry (VISR) has been proposed as a means to quantify the combustion efficiency (CE) of flares. This work presents a numerical assessment of VISR using computational fluid dynamics simulations of a steam-assisted industrial flare, with a focus on three aspects: how approximations in the spectroscopic model impact the local “pixel-wise” CE, the validity of the approach for computing flare global CE using inferred local CE values, and the ability and limitations of VISR instrument to capture fuel that may be aerodynamically stripped from the combustion zone under crosswind conditions. The present analysis is conducted using simulated images generated over bands aligned with absorption features of three key products of flare combustion: CO2 (4.2–4.4 µm), CO (4.5–4.9 µm), and CH4 (3.2–3.4 µm). The results show that the simplified VISR approach can predict local CE accurately, but the model used to convert these values into a flare global CE is flawed and potentially leads to large biases. Finally, since the technique relies on mid-infrared imaging, it is likely incapable of quantifying unburned (cold) methane that may be stripped from the combustion zone due to the presence of a high crosswind over the flare stack, leading to a significant overestimation of the actual flare performance.Implications Statement A technique called “Video imaging spectro-radiometry” (VISR) has been developed for quantifying the combustion efficiency of flares based on spectrally resolved imaging. In the original version of this technique, a multispectral camera measures emissions over spectral bands aligned with key absorption features of CO2, CO, and the C-H stretch absorption band of alkanes. A local combustion efficiency map is defined from the ratio of the broadband pixel intensities, which is then converted into an overall combustion efficiency through pixel-averaging.While this technique has been validated through extractive sampling studies, in this work we analyze simulated measurements using a CFD simulated steam-assisted flare. In this context the CFD data serves as a ground truth. The results call into question the veracity of the instrument model used to convert the local CE estimates into a global CE for the flare, as well as the ability of this technique to capture cold methane that may be diverted from the combustion zone through aerodynamic stripping. These findings have important implications for emerging technology-based emission regulations, as well as the development of new remote sensing technologies for measuring flare performance.

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