(599ab) Use Dynamic Simulation to Minimize Flare Emissions During Ethylene Plant Shutdown

There are large amount of emissions from flare during startup, shutdown and upset of an ethylene plant. Literature survey shows a shutdown procedure of a 300 kt ethylene emits about 150 ton of hydrocarbon through flare. Based on the 98% combustion efficiency that EPA recommended, it emits 1.2 ton of carbon monoxide, 0.22 ton of nitrogen oxides (NOx) and 3.4 ton of volatile organic compounds (VOCs). Since flare emissions happen within a short time, they will cause big impact on ambient air quality.

In this paper, dynamic simulation was used for shutdown procedure of an ethylene plant. Rigorous dynamic models were built, which included charge gas compressor (CGC), chilling train, demethanizer, deethanizer, depropanizer, hydrogenation reactor, ethylene splitter, propylene splitter, debutanizer and depentanizer. The shutdown procedure included many stages, and each stage had one or more dynamic models. Through dynamic simulation, a new shutdown procedure was proposed, which would decrease flare emissions by 50%. The new procedure was accepted by the ethylene plant and will be used for their next shutdown.