(256b) CFD and Response Surface Modeling of Flare Performance: DRE/CE Vs. Soot

As indicated in recent TCEQ and EPA reports, the flare destruction and removal efficiency (DRE) and combustion efficiency (CE) can drop below the 98% threshold under certain high air/steam-assisted conditions even in compliance with 40 CFR 60.18.  Flare operators have a special concern about soot emission, i.e., to avoid visible smoke to comply with EPA's visibility regulations.  In this work, the width of the operating window for flares to minimize soot emissions (i.e. be "smoke-free") while maintaining high destruction efficiencies (e.g., DRE>98%, CE>96.5%) will be discussed. A response surface model based on experimental flare efficiencies and soot emission data and correlating DRE/CE/soot to vent gas composition, heating value, steam/air injection, tip diameter, and jet velocity will be presented.   Combustion mechanisms with soot precursor species developed using CHEMKIN were deployed in conjunction with soot models built in FLUENT. Computational fluid dynamics (CFD) software, FLUENT, were used to model flare cases in 2010 TCEQ flare study as well as in 1983/1984 EPA flare studies for which soot/DRE/CE data are available.  These data will be used to select combustion mechanism, soot/turbulence/turbulence-chemistry interaction models, and model parameters. The CFD results will be compared with experimental industrial/laboratory scale flare soot/DRE/CE data.  

This work presents a unique forum to discuss the potential trade-offs in emissions at different operating conditions, and ultimately to develop optimal control strategies to maximize environmental performance.