(26c) Innovative Stripper Revamp Improves Hydrocracker Operation

Valero Port Arthur refinery operates a 40 MBD Hydrocracker that has a front-end
stripper. After the passing through the conversion reactors, the Stripper removes the
light hydrocarbons (butane and lighter, including Hydrogen Sulfide) from the bottoms
product. The bottoms product is further processed into finished blendstocks in the
downstream Product Fractionator.

The original Stripper design included packed sections above and below the feed zone.
The Stripper never operated well and prevented the Fractionator Light Naphtha from
meeting specifications. Feed zone distributor and packing fouling and subsequent
flooding was identified as problem areas. This limited Hydrocracker rate and conversion
and frequently resulted in refinery slowdowns due to Stripper liquid carryover.

During a 2009 turnaround, the bottom of the Stripper was revamped from two
beds of packing to trays. The revamp utilized a novel support system that stacked
approximately 10-12 trays on a single support ring, and did not require welding to
the tower shell. The two-pass trays were supported from surrogate rings and support
pedestals which were sandwiched together. Packing removal and tray installation was
accomplished in 8.5 days, which was only slightly longer than the previous packing
replacement turnaround duration.

After almost a year of operation, post-revamp data indicates that the trays are
performing much better than the packing. There is no evidence of fouling degradation,
the Fractionator Light Naphtha sulfur content has decreased from 90-100 ppm to 5-10
ppm, and Stripper flooding has been eliminated. The authors will present pre-revamp
data, describe the revamp strategy, and present post-revamp data that will show that

trays were the best choice for this high liquid rate/low vapor rate service.