So, you want to measure flare emissions? Challenges and opportunities for quantifying utility pipe flare performance

Flares are critical for the safe destruction of waste gases and must operate effectively over a broad range of conditions. Even at low gas flow rates, the flames created by flares are highly turbulent and exhibit significant transient behavior, yet few studies report time-resolved emission data. This work presents spatially- and temporally-resolved experimental and computational results for gas-phase emissions from a utility-pipe flare (7.62 cm diameter) under varying crosswind speeds. Emissions measurements are presented for high and low combustion efficiency (CE) using natural gas and a propane and natural gas blend. The experiments considered flow rates of 98 liters per minute (LPM) for natural gas with crosswind speeds of 0.3 m/s (CE = 100 % ± 0.03 %) and 10 m/s (CE = 80.2 % ± 2.46 %). The propane and natural gas blend experiments were conducted at a flow rate of 490 LPM and crosswind speeds of 8.8 m/s (CE = 94.3 % ± 2.71 %) and 16 m/s (CE = 88.0 % ± 2.71 %). Large-eddy simulations (LES) of methane at 830 LPM with crosswind speeds of 3 to 12 m/s yielded CE values from 99.45 % to 95.89 %. Both experiments and LES demonstrate that severe thermal and species gradients persist well downstream of the primary combustion zone. LES further reveals that local CE can deviate significantly from global CE, underscoring potential limitations of emissions measurement approaches. The findings provide a benchmark data set for flare emissions under crosswind conditions and highlight the need to refine existing analytical methods while guiding the development of next-generation measurement strategies.