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Maximum Exit Velocity for Stability (ft/sec)

FIG. 5.21.7 Flame stability limits for different gas mixtures flared without pilot assist from a 3-in open-pipe nozzle.

crease in the heating value of the waste to maintain a stable flame. For Cl-containing compounds, the flame stability should correlate with the H/Cl ratio.

Stone et al. (1992) outline design procedures for flares. The U.S. EPA requirements for flares are specified in 40 CFR Section 60.18. The requirements are for steam-assisted, air-assisted, and nonassisted flares. For steam-assisted, elevated flares, the following points must be addressed:

An exit velocity at the flare tip <60 ft/sec (for 300 Btu/scf gas streams) and <40 ft/sec (for >1000 Btu/scf gas streams). Between 300-1000 Btu/scf, the following equation applies:

log Vmax =

NHV + 1214

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