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 instrument model used to convert these values into a flare global CE 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.<i>Implications</i>: Oil and gas producers and regulators increasingly rely on continuous monitoring emission systems to measure methane slip, e.g., under OGMP 2.0. However, the effectiveness of many of these techniques, particularly those based on spectroscopic principles, has yet to be established in a rigorous way, particularly given the uncertainties inherent in extractive monitoring. This paper presents a methodology that focuses on one emerging continuous monitoring technology and could be adapted as a general strategy for benchmarking the performance of continuous monitoring systems.