Vacuum Distillation In Petroleum Refinery

Vacuum distillation is the distillation of liquids carried out at a strain decrease than atmospheric strain to reap the benefits of the fact that reducing the stress lowers the boiling point of liquids.

Petroleum crude oil is a posh mixture of hundreds of various hydrocarbon compounds generally having from three to 60 carbon atoms per molecule, though there could also be small quantities of hydrocarbons exterior that range.[1][2][three]

The refining of petroleum crude oil begins with distilling the incoming crude oil in a so-referred to as atmospheric crude oil distillation unit (CDU) working at pressures slightly above atmospheric strain.[1][2][4] In distilling the crude oil, it will be important to not subject the crude oil to temperatures above 370 to 380 °C as a result of the excessive molecular weight parts in the crude oil will endure thermal cracking and form petroleum coke at temperatures above that.

The formation of coke is very undesirable and would result in plugging the tubes within the furnace that heats the feed stream to the crude oil distillation column. Plugging would additionally happen within the piping from the furnace to the distillation column as well as in the column itself.

The constraint imposed by limiting the column inlet crude oil to a temperature of lower than than 370 to 380 °C yields a residual oil from the underside of the atmospheric distillation column consisting solely of hydrocarbons that boil above 370 to 380 °C.

To additional distill the residual oil from the crude oil distillation unit, the distillation is performed at absolute pressures as little as 10 to forty mmHg (additionally referred to as torr) in order to limit the working temperature to less than 370 to 380 °C.

Figure 1 is a photograph of a big vacuum distillation column in a petroleum refinery and Determine 2 is a schematic process flow diagram of a petroleum refinery vacuum distillation column that depicts the internals of the column.

The ten to forty mmHg absolute strain in a vacuum distillation column will increase the volume of vapor formed per quantity of liquid distilled. The result is that such columns have very giant diameters.[5] Vacuum distillation columns, such these in Images 1 and 2, might have diameters of 15 meters or more, heights ranging as much as about 50 meters, and feed rates ranging as much as about 25,four hundred cubic meters per day (160,000 barrels per day).

The vacuum distillation column internals should present good vapor-liquid contacting while, at the identical time, sustaining a really low pressure increase from the column high to the column bottom. Due to this fact, refinery vacuum columns usually use distillation trays only the place withdrawing merchandise from the aspect of the column (referred to as aspect draws). The remainder of the column uses packing materials for the vapor-liquid contacting because such packing has a lower stress drop than distillation trays. This packing materials will be both structured sheet steel or randomly dumped packing comparable to Raschig rings.

Absolutely the pressure of 10 to 40 mmHg in a refinery vacuum distillation column is most frequently achieved by a vacuum system using multiple levels of steam jet ejectors.[6][7]

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Many industries, apart from the petroleum refining industry, use vacuum distillation on a much smaller scale.

  1. J.H. Gary and G.E. Handwerk (1984), Petroleum Refining Technology and Economics, 2nd Version, Marcel Dekker, Inc. ISBN zero-8247-7150-eight.
  2. W.L. Leffler (1985), Petroleum refining for the nontechnical particular person, 2nd Version, PennWell Books. ISBN zero-87814-280-zero.
  3. James G. Speight (2006), The Chemistry and Know-how of Petroleum, Fourth Edition, CRC Press. 0-8493-9067-2.
  4. Henry Z. Kister (1992), Distillation Design, 1st Version, McGraw-Hill. ISBN zero-07-034909-6.
  5. Karl Kolmetz, Andrew W. Sloley et al (2004), “Designing Distillation Columns for Vacuum Service”, 11th India Oil and Gas Symposium and International Exhibition, Mumbai, India (also revealed in Hydrocarbon Processing, Might 2005).
  6. Robert B. Power (1993), Steam Jet Ejectors For The method Industries, First Version, McGraw-Hill. ISBN zero-07-050618-3.
  7. Editor:Richard Darton (1997), Distillation and Absorption, Volume 2, First Edition, web page 594, Establishment of Chemical Engineers, United Kingdom. ISBN 0-85295-393-3.

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