(175c) Vacuum Distillation: Slop Wax Disposition

Refinery vacuum units include a deentrainment, or wash zone, for removal of heavy material from desired products. A continuous wash oil stream prevents the wash zone (deentrainment zone) from coking. Underneath the wash zone a collector tray gathers the liquid from the wash zone plus any entrainment removed. The total liquid collected on this tray is called slop wax.

Traditionally, slop wax has been drawn from the vacuum tower as a stream and recycled to the feed upstream of the vacuum feed heater. Less common alternate dispositions include sending the slop wax to a stripping section inside the vacuum tower or making the slop wax a product stream.

This review covers:

• Survey of operating units to identify the most common slop wax dispositions.
• Evaluation of the major options for towers without stripping sections.
• Evaluation of the major options for towers with stripping sections.
• Review of the effect of entrainment on slop wax dispositions.