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Naphthenic Distillates: Reduced Crude Cut by Viscosity in a Vacuum Tower (Armstrong 1965)
Charlie

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Charlie

28. October 2026DE
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Naphthenic Distillates: Reduced Crude Cut by Viscosity in a Vacuum Tower (Armstrong 1965)

A wax-free naphthenic crude, stripped of its gasoline and naphtha, goes into a vacuum tower as hot vapour. Caustic soda near the bottom takes out its acids as a sludge. Five lubricating oils are drawn off the side of the tower, each held to its own viscosity. These are naphthenic distillates, the feed for white mineral oil. Source: C. R. Armstrong (Sun Oil Company), US 3,184,396 (1965), a Sun Oil tower of 39 trays and 12,000 barrels a day. He does not give the crude tower's conditions, how the feed is heated or how much caustic is used. The steam boiler and hydrometer are ours. The picture: the patent's Fig. 1.
Advanced
continuous

Instructions

1

Top the crude

Take a wax-free naphthenic crude. Armstrong's crudes were sorted and blended to give lubricating oils with a viscosity-gravity constant of 0.885–0.893. Strip off the low-boiling part (straight-run gasoline, naphtha) in a separate crude tower; the patent gives no conditions for it. What is left is the "reduced" crude.

Materials for this step:

Naphthenic Crude OilNaphthenic Crude Oil1 as required

Tools needed:

Atmospheric Distillation ColumnAtmospheric Distillation Column
2

Lay out the vacuum tower

Armstrong's tower has 39 trays, 20 ft across and 128 ft high. Take-offs, counted from the bottom: gas oil overhead at tray 35, through a condenser to an accumulator, part of it sent back as reflux to hold the top temperature; transformer oil ("Transoil") at tray 29; 91-G at tray 26; 94-G below it, partly cooled in a heat exchanger and returned as reflux; 96-G at tray 19; 87-Red at tray 16. Tray 7 is a total trap-out tray with a demister above it: between them is the caustic section.

Tools needed:

Vacuum Distillation ColumnVacuum Distillation Column
Condenser CoilCondenser Coil
Heat ExchangerHeat Exchanger
3

Pull the vacuum

Hold the top of the tower at 15–20 mm of mercury absolute with steam jet ejectors and barometric condensers. Ours: a steam boiler for the jets.

Tools needed:

Steam Jet EjectorSteam Jet Ejector
Barometric CondenserBarometric Condenser
Steam BoilerSteam Boiler
Pressure GaugePressure Gauge
4

Feed the reduced crude as vapour

Charge the reduced crude near the bottom, below tray 7, at about 650 °F (343 °C), so it enters as vapour. The patent does not say how it is heated. Whatever does not vaporise runs down and is drawn off as tower bottoms, by level.

Tools needed:

Vacuum Distillation ColumnVacuum Distillation Column
Thermocouple with ReadoutThermocouple with Readout
5

Feed caustic soda into the caustic section

Feed fresh caustic soda, 50° Baumé for example, at tray 10. It turns the acidic parts of the vapour into a sodium salt that does not boil, and this collects as a sludge on tray 7. Take some sludge off tray 7 and return it at tray 10 to stir it; leave some 87-Red in the tower to thin it so the section does not plug. Draw the sludge off by level. Ours: a hydrometer to check the Baumé.

Tools needed:

Sodium Hydroxide SolutionSodium Hydroxide Solution
HydrometerHydrometer
Vacuum Distillation ColumnVacuum Distillation Column
6

Hold each side stream to its viscosity

Measure each side stream with a viscometer: Transoil 55 S.S.U. at 100 °F (38 °C); 91-G 105 S.S.U. at 100 °F; 94-G 500 S.S.U. at 100 °F; 96-G 90 at 210 °F (99 °C); 87-Red 150 at 210 °F. Correct a stream by the draw-off of the stream just above it: Transoil by the gas oil. If a stream runs thick, draw more from the one above, so its lighter parts come down. Set 87-Red by hand.

Tools needed:

ViscometerViscometer
Vacuum Distillation ColumnVacuum Distillation Column
7

Run the on-spec oils to storage

Send only side streams that are on viscosity to storage. Each of the five lubricating oils is a naphthenic distillate. The gas oil, the sludge and the bottoms take the rest of the feed.

Tools needed:

ViscometerViscometer
Vacuum Distillation ColumnVacuum Distillation Column

Materials

1

Tools Required

12

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