Reduced Flaring Options during Ethylene Plant Start-up and Shutdown

Ethylene producers and licensors are facing the challenge posed by the environmental regulations to minimize the emissions of Highly Reactive Volatile Organic Compounds (HRVOCs) during plant start-up, shutdown and emergency conditions, as well as the economic loss from the flaring of valuable feedstock. For many years, various strategies have been employed to minimize flaring, with varying success.

TechnipFMC Process Technology (PT) has developed a scheme/strategy to minimize the flaring, which would also help to reduce the steam import requirements at very high pressure (VHP) level, required to start the main process compressors. The strategy is also aimed at reducing flaring during the preparation for the scheduled turn around / shutdown; purging the system of benzene while shutting down various units and reducing the number of days required for maintenance preparation.

Various other recycle lines are added to allow for chill down, establish circulation through the plant and stabilize various plant sections prior to the fresh feed introduction to the furnaces. This makes the unit ready to receive fresh feed and process the cracked gas to minimize the time required to achieve on-spec production. The basic concept presented reflects operation of the Cracked Gas Compressor on Nitrogen or Methane rich natural gas, with provision to circulate through the feed system. The flow scheme provides the flexibility to circulate through the Cracking Furnaces, which allows for the generation of VHP steam.

The scheme presented here-in is for an Ethane Cracker but the concepts can be customized for liquid cracker schemes to meet the specific requirements and applicable conditions. Existing plants can also be retrofitted to implement many of these concepts, to reduce flaring and improve the profitability.