User:Milton Beychok/Sandbox: Difference between revisions
imported>Milton Beychok |
imported>Milton Beychok No edit summary |
||
| Line 9: | Line 9: | ||
[[Petroleum crude oil]] is a complex mixture of hundreds of different [[hydrocarbon]] compounds generally having from 3 to 60 carbon atoms per molecule, although there may be small amounts of hydrocarbons outside that range.<ref name=Handwerk>{{cite book|author=Gary, J.H. and Handwerk, G.E.|title=Petroleum Refining Technology and Economics|edition=2nd Edition|publisher=Marcel Dekker, Inc|year=1984|id=ISBN 0-8247-7150-8}}</ref><ref name=Leffler>{{cite book|author=Leffler, W.L. |title=Petroleum refining for the nontechnical person|edition=2nd Edition|publisher=PennWell Books|year=1985|id=ISBN 0-87814-280-0}}</ref><ref>{{cite book|author=James G, Speight|title=The Chemistry and Technology of Petroleum|edition=Fourth Edition|publisher=CRC Press|year=2006|id=0-8493-9067-2}}</ref> In refining the crude oil, it is important not to subject the high [[molecular weight]] components to temperatures above 370 to 380 °C because they will undergo [[thermal cracking]] and form [[petroleum coke]] at temperatures above that. Formation of coke would result in plugging the tubes in the [[furnace]] that heats the feed stream to a column distilling either the whole crude oil or only the higher molecular weight components of crude oil. Plugging would also occur in the [[piping]] from the furnace to the distillation column as well as in the column itself. | [[Petroleum crude oil]] is a complex mixture of hundreds of different [[hydrocarbon]] compounds generally having from 3 to 60 carbon atoms per molecule, although there may be small amounts of hydrocarbons outside that range.<ref name=Handwerk>{{cite book|author=Gary, J.H. and Handwerk, G.E.|title=Petroleum Refining Technology and Economics|edition=2nd Edition|publisher=Marcel Dekker, Inc|year=1984|id=ISBN 0-8247-7150-8}}</ref><ref name=Leffler>{{cite book|author=Leffler, W.L. |title=Petroleum refining for the nontechnical person|edition=2nd Edition|publisher=PennWell Books|year=1985|id=ISBN 0-87814-280-0}}</ref><ref>{{cite book|author=James G, Speight|title=The Chemistry and Technology of Petroleum|edition=Fourth Edition|publisher=CRC Press|year=2006|id=0-8493-9067-2}}</ref> In refining the crude oil, it is important not to subject the high [[molecular weight]] components to temperatures above 370 to 380 °C because they will undergo [[thermal cracking]] and form [[petroleum coke]] at temperatures above that. Formation of coke would result in plugging the tubes in the [[furnace]] that heats the feed stream to a column distilling either the whole crude oil or only the higher molecular weight components of crude oil. Plugging would also occur in the [[piping]] from the furnace to the distillation column as well as in the column itself. | ||
The refining of crude oil begins with distilling the incoming crude oil in a so-called [[Petroleum refining processes#The crude oil distillation unit|''atmospheric distillation column'']] operating at pressures slightly above atmospheric pressure.<ref name=Handwerk/><ref name=Leffler/><ref name=Kister>{{cite book|author=Kister, Henry Z.|title= | The refining of crude oil begins with distilling the incoming crude oil in a so-called [[Petroleum refining processes#The crude oil distillation unit|''atmospheric distillation column'']] operating at pressures slightly above atmospheric pressure.<ref name=Handwerk/><ref name=Leffler/><ref name=Kister>{{cite book|author=Kister, Henry Z.|title=Distillation Design|edition=1st Edition |publisher=McGraw-Hill|year=1992|id=ISBN 0-07-034909-6}}</ref> The constraint imposed by limiting the column inlet<br>temperature to no more than 370 to 380 °C yields a residual oil from the bottom of the atmospheric distillation column consisting entirely of hydrocarbons that boil above 370 to 380 °C. | ||
To further distill the residual oil from the atmospheric distillation column, the distillation must be performed at [[absolute pressure]]s as low as 10 to 40 [[mmHg]] (also referred to as [[Torr]]) so as to limit the operating temperature to less than 370 to 380 °C. | To further distill the residual oil from the atmospheric distillation column, the distillation must be performed at [[absolute pressure]]s as low as 10 to 40 [[mmHg]] (also referred to as [[Torr]]) so as to limit the operating temperature to less than 370 to 380 °C. | ||
| Line 15: | Line 15: | ||
Figure 1 is a photograph of a large vacuum distillation column in a petroleum refinery and Figure 2 is a process diagram of a petroleum refinery vacuum distillation column that depicts the internals of the column. | Figure 1 is a photograph of a large vacuum distillation column in a petroleum refinery and Figure 2 is a process diagram of a petroleum refinery vacuum distillation column that depicts the internals of the column. | ||
The 10 to 40 mmHg absolute pressure in a vacuum distillation column increases the volume of vapor formed per volume of liquid distilled. The result is that such columns have | The 10 to 40 mmHg absolute pressure in a vacuum distillation column increases the volume of vapor formed per volume of liquid distilled. The result is that such columns have very large diameters.<ref>Karl Kolmetz, Andrew W. Sloley et al (2004), ''Designing Distillation Columns for Vacuum Service'', 11th India Oil and Gas Symposium and International Exhibition, September 2004, [[Mumbai]], [[India]] (also published in ''Hydrocarbon Processing'', May 2005)</ref> | ||
Distillation columns such those in Figures 1 and 2, may have diameters of 15 meters or more, heights ranging up to about 50 meters, and feed rates ranging up to about 25,400 cubic meters per day (160,000 barrels per day). | Distillation columns such those in Figures 1 and 2, may have diameters of 15 meters or more, heights ranging up to about 50 meters, and feed rates ranging up to about 25,400 cubic meters per day (160,000 barrels per day). | ||
Revision as of 19:19, 9 February 2008
Vacuum distillation is distillation of liquids performed at a pressure lower than atmospheric pressure to take advantage of the fact that reducing the pressure lowers the boiling point of liquids. This permits the distillation of liquids that are temperature sensitive and avoids any degradation of such liquids.
Vacuum distillation in petroleum refining
Petroleum crude oil is a complex mixture of hundreds of different hydrocarbon compounds generally having from 3 to 60 carbon atoms per molecule, although there may be small amounts of hydrocarbons outside that range.[1][2][3] In refining the crude oil, it is important not to subject the high molecular weight components to temperatures above 370 to 380 °C because they will undergo thermal cracking and form petroleum coke at temperatures above that. Formation of coke would result in plugging the tubes in the furnace that heats the feed stream to a column distilling either the whole crude oil or only the higher molecular weight components of crude oil. Plugging would also occur in the piping from the furnace to the distillation column as well as in the column itself.
The refining of crude oil begins with distilling the incoming crude oil in a so-called atmospheric distillation column operating at pressures slightly above atmospheric pressure.[1][2][4] The constraint imposed by limiting the column inlet
temperature to no more than 370 to 380 °C yields a residual oil from the bottom of the atmospheric distillation column consisting entirely of hydrocarbons that boil above 370 to 380 °C.
To further distill the residual oil from the atmospheric distillation column, the distillation must be performed at absolute pressures as low as 10 to 40 mmHg (also referred to as Torr) so as to limit the operating temperature to less than 370 to 380 °C.
Figure 1 is a photograph of a large vacuum distillation column in a petroleum refinery and Figure 2 is a process diagram of a petroleum refinery vacuum distillation column that depicts the internals of the column.
The 10 to 40 mmHg absolute pressure in a vacuum distillation column increases the volume of vapor formed per volume of liquid distilled. The result is that such columns have very large diameters.[5]
Distillation columns such those in Figures 1 and 2, may have diameters of 15 meters or more, heights ranging up to about 50 meters, and feed rates ranging up to about 25,400 cubic meters per day (160,000 barrels per day).
The vacuum distillation column internals must provide good vapor-liquid contacting while, at the same time, maintaining a very low pressure increase from the top of the column top to the bottom. Therefore, the vacuum column uses distillation trays only where withdrawing products from the side of the column (referred to as side draws). Most of the column uses packing material for the vapor-liquid contacting because such packing has a lower pressure drop than distillation trays. This packing material can be either structured sheet metal or randomly dumped packing such as Raschig rings.
The absolute pressure of 10 to 40 mmHg in the vacuum column is most often achieved by using multiple stages of steam jet ejectors. [6]
Many industries, other than the petroleum refining industry, use vacuum distillation on a much a smaller scale.
Laboratory-scale vacuum distillation
References
- ↑ 1.0 1.1 Gary, J.H. and Handwerk, G.E. (1984). Petroleum Refining Technology and Economics, 2nd Edition. Marcel Dekker, Inc. ISBN 0-8247-7150-8.
- ↑ 2.0 2.1 Leffler, W.L. (1985). Petroleum refining for the nontechnical person, 2nd Edition. PennWell Books. ISBN 0-87814-280-0.
- ↑ James G, Speight (2006). The Chemistry and Technology of Petroleum, Fourth Edition. CRC Press. 0-8493-9067-2.
- ↑ Kister, Henry Z. (1992). Distillation Design, 1st Edition. McGraw-Hill. ISBN 0-07-034909-6.
- ↑ Karl Kolmetz, Andrew W. Sloley et al (2004), Designing Distillation Columns for Vacuum Service, 11th India Oil and Gas Symposium and International Exhibition, September 2004, Mumbai, India (also published in Hydrocarbon Processing, May 2005)
- ↑ Photo gallery (from website of Graham Manufacturing Company)
- ↑ Vacuum Distillation: New Method for Analyzing Organic Chemicals in a Wide Array of Samples (United States Environmental Protection Agency)
- ↑ What is vacuum distillation? (Argonne National Laboratory's NEWTON Ask-A-Scientist)