Air-Quality Evaluation on Flare Minimization Strategies for an Ethylene Plant Shutdown

Flare emissions from chemical plants inevitably affect air quality of their surrounding regions.  Intensive flare emission events, such as ethylene plant shutdown, emitting huge amounts of VOCs and NO_X in a short-time period, have great potentials to increase the regional ozone concentration in transient time.  Thus, the developed flare minimization strategy for a plant shutdown is better to be evaluated on its potential air-quality impact.

In this paper, dynamic simulations are employed to model two scenarios of shutdown for characterizing the emission information including flow rate and speciation.  Firstly, a base case of shutdown strategy is simulated and its dynamic emission profile is generated. Secondly, the optimal shutdown strategy is simulated to recover more liquid and vapor hydrocarbon materials in the facilities.  Compared with the base case, the optimal shutdown strategy includes certain flare reduction measures.  The obtained flaring emissions were then incorporated into a CAMx air-quality simulation model to simulate the impact from these extra VOCs and NO_X emissions on the regional ozone concentrations.  The increments of hourly ozone concentration from the base case are observed as high as 35 ppb; while those from the optimal shutdown strategy are relatively low in both spatial and temporal domains.