(497f) Simultaneous Reduction of Chemical Plant Start-Up Flaring and Regional Air Quality Impact Via Multi-Scale Dynamic Modeling

Chemical plant flaring during malfunction, startup and shutdown (MSS) generates large amounts of air emissions in a relatively short period of time, and  cause the local areas to have high concentrations of air pollutants, which adversely impact the health of people nearby and contribute to smog (caused by ozone) and other problems in communities that are further downwind. Releases of air pollutants that result from MSS have been of great concern and interest to both state and federal regulators. Flare minimization technique through dynamic process simulation has been recognized as a cost-effective method to reduce flaring emission by evaluating potential process and procedural modifications prior to the actual shutdown/startup or malfunction event. Based on  plant-wide dynamic simulation, flaring emission associated with different startup strategies can be quantified and characterized. However, the air quality impact of a specific startup scenario should not be easily assessed by comparing the total amount of emissions or VOC species. Thus, multi-scale dynamic modeling system based on the combination of dynamic process model and air quality model is built to realize that chemical plant startup flaring and regional air quality impact can be reduced simultaneously.

In this paper, an ethylene plant with different startup scenario has been investigated through both dynamic process model and air quality model. In the dynamic process model, plant-wide dynamic simulations are employed to model different startup strategies. Several feasible strategies can be identified to optimize startup procedures and realize the flaring reduction. The emission profile with characterization during startup can be obtained. In the air quality model, the obtained flaring emissions were then incorporated into a CAMx 3-D air quality model to simulate the effect of these extra VOCs and NO_X emissions on the regional ozone concentrations. The effects of startup starting time, plant location, and episode day on ozone increments with various startup scenarios were investigated and scientific insights were provided. The environmentally conscious startup schedule is the one that avoids having the peak flaring emissions occur near the time of the highest solar intensity to minimize the impact of the startup process on the regional ozone concentrations.