Vacuum tower feed, naphtha

Too much naphtha in the vacuum tower feed made it impossible for the vacuum condensate seal drum slop pumps to keep the level under control. Turning on the spare pump did not help, as both pumps were operating on the flat portion of their performance curves. 

To distill most of the gas oil out of the crude while still avoiding excessive temperatures, a vacuum tower is used. The crude unit s primary tower is intended to fractionate between naphtha, kerosene, and furnace oil. The vacuum tower only has one function to produce a clean, high-boiling gas oil suitable for cracking-plant or lube-oils refining feed. 

In the process (Figure 9-22), fresh vacuum residuum, microcatalyst, and hydrogen are fed to the hydroconversion reactor. Effluent is sent to a flash separation zone to recover hydrogen, gases, and liquid products, including naphtha, distillate, and gas oil. The liquid bottoms from the flash step is then fed to a vacuum distillation tower to obtain a 565°C (1050°F ) product oil and a 565°C + (1050°F+) bottoms fraction that contains unconverted feed, microcatalyst, and essentially all of the feed metals. 

The overhead product from the primary tower is divided into an overhead and a bottom product in the secondary tower, which operates under a partial vacuum with steam injected into the bottom of the tower to assist in the fractionation. The overhead and bottom products are finished aliphatic solvents, or if the feed to the primary tower is light naphtha instead of heavy naphtha, other aliphatic solvents of different boiling ranges are produced. 

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