(33e) Flux Oil Stream Import to Quench System - Risks & Impacts

External flux oil import to the primary fractionator is a known practice in ethylene plant.  The typical situations where external flux oil might be used include start up and correction of deficiencies in quench oil characteristics often required due to major changes in feedstock slates and quality.  One of the major risks of mixing external oil with fuel oil generated from the cracking heaters is precipitation of ashphaltene-like, large polynuclear aromatic species (PNA).  Oil incompatibility can lead to severe fouling of the quench oil loop, increased viscosity, and potentially result in a total plant shut down. Proper characterization of the flux oil and evaluation of its compatibility with the fuel oil is a key element in achieving the desire objectives. This paper discusses the preferred characteristics of external flux oil and compatibility testing that helps its selection.  Results from simulation work are also presented to highlight the slow response of the system and relatively high residence time of oil components in the quench oil loop. A few case studies are also presented.