(63d) Impact of Flaring Emissions on Regional Air Quality Associated with An Ethylene Plant Start-up

Flaring is a common industrial practice designed to eliminate the accumulation of un-reacted feed gases or off-specification product gases through stack burning to ease the strain on a process unit especially during plant start-ups, plant shut-downs and operational up-sets. Although the practice is necessary and crucial to chemical plant safety, excessive flaring represents the loss of precious feed materials and also results in the generation of extra amounts of undesired emissions including VOCs and NO_X, both of which are ozone precursors.

In this study, the effects of flaring emissions associated with an ethylene plant start-up with various start-up scenarios on the increment of regional ozone concentrations were investigated through model simulations.  In the practice, the dynamic process simulations associated with an ethylene plant start-up were performed first.  The obtained flaring emissions were then incorporated into a CAMx air quality simulation model to simulate the effect of these extra VOCs and NO_X emissions on the regional ozone concentrations.  From the the CAMx simulations, the effects of start-up starting time, plant location, and episode day on ozone increments associated with various start-up scenarios were investigated and scientific insights were also provided.  Finally, the environmentally-preferred start-up schedule is identified as the one that avoids having the peak flaring emissions occur near the time of the highest solar intensity to minimize the impact of the start-up process on the regional ozone concentrations.