Acetylene Converter Operational Risk Mitigation in Front-End Reactors

Ethylene production requires removal of all acetylene produced in the cracking process before its use in subsequent chemicals manufacturing. Most commonly accomplished by catalytic hydrogenation, a challenge in “front-end” process configuration is the acetylene must be selectively reacted from a stream where hydrogen can be present in a >300X molar excess and ethylene present in a >100X molar excess to acetylene in the reactor inlet. Since both the selective hydrogenation of acetylene to ethylene and the non-selective hydrogenation of ethylene to ethane are highly exothermic reactions, high bed temperatures and thermal runaway events are possible in adiabatic reactor configurations when hydrogenation reaction rates are not maintained by proper operation control. Unplanned and uncontrolled thermal excursions in the hydrogenation reactor results in production downtime, product flaring, can irreparably damage the catalyst requiring a unit shutdown for catalyst change, and can lead to process safety incidents where vessel integrity is compromised.

Since the “Front End” process configurations have been selected for most newer ethylene production units, awareness of historical operation experience is of value to those new to these processes. In this session, we will review the fundamentals of “front-end” selective hydrogenation, survey the operational mechanisms and causes of runway reactions, and discuss risk awareness and mitigation opportunities via system controls, operational considerations, and catalyst behavior to improve inherent safety and operating reliability.