Revamping of Distillation and Rectification Sections

Major oil refinery plant

Column name:
Vacuum oil column

Column diameter:

Production Problems
Often standard trays were applied in the column; this resulted in poor efficiency, high pressure drop, low yield of oil fraction and wide range of fraction. Moreover, due to improper column operation the colour of oil fraction remained deep; the content of residual deposition is high.

Column's Performance
This column is the largest-scale vacuum oil column in China. At first R-K trays with 3,500,000 tons per year oil refinery capacity were applied in the column. At the end of 80-s the bottom of the column was revamped with regular structured packing with the help of well-known American company in order to increase heavy fraction. Some years afterwards an accident happened during the maintenance as a result the packing was broken as well as the interior structures. Thereafter one local company rehabilitated the broken packing and column internals but for some reason the performance characteristics were not fully restored.

Revamping Works
Dump packing at the bottom of the column and two oil collectors were not renovated in order to save expenses. Inlet distributor was a little bit changed to increase the distribution effect. Side-cut distillates were not changed. High-efficiency regular structured packing was applied for all six packing layers, this is tantamount to twenty-three theoretical trays. The packing has been specially surfaced to speed up skin formation that gives more N15 than standard regular structured packing. Special channel type liquid distributors were designed for equal liquid distribution through all the seven packing layers. The up-to-date oil collectors were designed to improve vapour distribution at minimum pressure drop. Special liquid collectors were used to guarantee equal liquid level in the main tank. Inside cylinder was designed for flushing section to increase the liquid flow rate in the layer.

Revamping Results
Under normal operation of the column pressure drop reduced to 20 mm Нg, boiling range of all side-cut distillates contracted. Colority and CCR content of heavy fraction was significantly improved. Fraction < 500°С in the vacuum residue decreased from 7% to 4%.