(34b) Upgrading a Vacuum Tower at a Major South East Refinery

Many existing vacuum towers have been revamped to boost the capacity and or to increase the cut point more than once since their first start up. In most of the cases, only the mass transfer components of the vacuum column were upgraded. Fractionation trays were replaced with random packing, and subsequently with structured packing to minimize the pressure drop and thus the pressure at the flash zone with the final goals of maximizing throughput and distillates recovery.

Indeed rarely these revamps have addressed also a proper check of the fired heater, the transfer line, and the feed entry lay out to the flash zone of the vacuum tower. The increased throughput and reduced pressure will cause an increasing of the volume while the feed is traveling from the furnace coil outlet to the flash zone of the tower. A proper check of the velocity profile through the entire transfer line is mandatory to avoid the draw back associated to the risk of approaching the critical velocity at which, a consistent reduction of distillates yields may occur, or even mechanical damages.

This paper will describe the revamp of a vacuum tower at a major south east refinery where the transfer line of the fired heater was re-routed as the feed nozzle to the vacuum tower was relocated from tangential to radial. A detailed comparison of the operating data before and after the revamp will be also shown.