Risk of Runaway in Backend Acetylene Converters

In the “Tail End” process configuration the cracked gas light ends are removed downstream of the cold box and acetylene hydrogenation is completed at the De-ethanizer overhead. The C2 fraction is combined with hydrogen upstream of the Acetylene Converter in stoichiometric H₂/Ac molar ratio control. This controlled addition of hydrogen to the reactor limits the extent of the hydrogenation reaction making a thermal runway reaction rare in “Tail End” operations. Nevertheless, runaway reactions have been observed in “Tail-end” processes when process design shortfall, mechanical failure or gross operational error have occurred. In such cases, uncontrolled hydrogen addition resulted in exothermic runway events.

“Tail End” operating units are still the predominant process for Ethylene production and a viable option for new ethylene units under construction design. It is therefore important to review the risk of run-away in these units. In this session we will review the fundamentals of “Tail End” acetylene hydrogenation, weigh potential causes of thermal runway in such units, share industrial experience of a runway event and present best practices to mitigate risk of run-away.