Efficiency Measurements of Flares in a Cross Flow

This paper presents results from experimental measurements of the combustion efficiencies of jet diffusion flames in a cross flow. The purpose for studying these flows is to understand and model the combustion of gas flares burning in the atmosphere. The experiments involve a jet of fuel gas that emerges from a circular tube that is oriented vertically in the test section of a wind tunnel and perpendicularly to the cross flow of air. The model flare stack is 25mm in diameter and extends approximately 20 diameters into the tunnel. Natural gas (~94% methane), commercial grade propane (~98% propane), and commercial grade propane diluted with up to 80% carbon dioxide were used as fuels. Experiments were performed with exit velocities of 0.5, 1.0, 2.0 and 4.0 m/s in cross flows as high as 16m/s. The overall combustion efficiencies of these flames, based on a gaseous carbon balance, were measured as a function of jet velocity, cross flow velocity, and volumetric energy content of the fuel gases. Results show that wind speed can have a profound effect on efficiency (i.e. efficiency drops by approximately the cube of wind speed) and that having higher jet exit velocities makes the flames less susceptible to these wind effects. As well, the data shows a dramatic decrease in combustion efficiency as the volumetric energy content of the fuel is reduced.