Ethylene producers and licensors are facing the challenge posed by the environmental regulations to minimize the emissions of Highly Reactive Volatile Organic Compounds (HRVOC’s) during plant start-ups, 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.
Technip Stone & Webster Process Technology has developed a scheme/strategy to minimize flaring. The scheme is designed to also help reduce steam import requirements at the 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 turnaround / shutdown, purging the system of benzene while shutting down various units and reducing the number of days required for maintenance preparation.
The basic concept presented is to start the Cracked Gas Compressors on methane rich natural gas and to circulate through the Cracking Furnaces, which allows for the generation of VHP steam. 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 scheme presented herein is for an Ethane Cracker but the concepts can be customized for other processing schemes to meet the client specific requirements and applicable conditions. Existing plants can also be retrofitted to implement many of these concepts, which will reduce flaring and improve profitability.