年處理量9萬噸苯——甲苯精餾浮閥塔設(shè)計(jì)（全套CAD圖+說明書+開題報(bào)告+翻譯）
年處理量9萬噸苯——甲苯精餾浮閥塔設(shè)計(jì)（全套CAD圖+說明書+開題報(bào)告+翻譯）,處理,萬噸苯,甲苯,精餾,浮閥塔,設(shè)計(jì),全套,cad,說明書,仿單,開題,報(bào)告,講演,呈文,翻譯
ExxonMobil Research & Engineering Company (P.O. Box 900, 1545 Route 22 East, Annandale, NJ, 08801-0900, US)
Claims:
What is claimed is:
1. A de-entrainment baffle for location in a distillation tower having a feed zone, a flash zone and a wash zone, the baffle comprising a plurality of radial fins with openings between the fins to permit the upward passage of vapors from the portion of the tower below the baffle.
2. A baffle according to claim 1, wherein each fin is angularly inclined with respect to a plane passing through a central axis of the baffle such that an upper edge of the fin is displaced relative to the lower edge in the direction of flow of incoming feed to the tower.
3. A baffle according to claim 2, wherein each fin is angularly inclined with respect to the plane passing through the central axis of the baffle such that the upper edge of the fin is displaced relative to the lower edge in the direction of flow of incoming feed to the tower by an angle from 0° to 180°.
4. A baffle according to claim 3, wherein the angle is between 30° to 60°.
5. A baffle according to claim 3, wherein the inclination of each fin relative to the central axis of the baffle is constant along the radial length of the fin.
6. A baffle according to claim 1, further comprising at least one liquid downcomer to permit downward passage of liquid past the baffle.
7. The baffle according to claim 6, wherein the at least one liquid downcomer is located in a central portion of the baffle.
8. The baffle according to claim 6, wherein the at least one liquid downcomer is offset from the center of the baffle.
9. The baffle according to claim 6, wherein the at least one liquid downcomer comprises two spaced apart liquid passageways.
10. The baffle according to claim 6, wherein the at least one liquid downcomer comprises at least two downcomers, wherein one downcomer is disposed at an angle with respect to another dowcomer.
11. The baffle according to claim 1, further comprising: a central circular hub; a peripheral collar spaced from the central circular hub, wherein the plurality of radial fins extend between the central hub and the peripheral collar.
12. A baffle according to claim 11, wherein the central hub comprises an open collar providing a liquid downcomer for passage of liquid downwards through the baffle.
13. A baffle according to claim 11, wherein the central hub comprises an upstanding circular wall member and a cover over the top of the wall member.
14. The baffle according to claim 11, further comprising: at least one intermediate collar spaced between the central circular hub and the periperhal collar.
15. The baffle according to claim 14, wherein a first set of fins extends between the central circular hub and one intermediate collar and a second set of fins extends between the intermediate collar and the peripheral collar.
16. The baffle according to claim 11, further comprising at least one liquid downcomer to permit downward passage of liquid past the baffle.
17. The baffle according to claim 16, wherein the at least one liquid downcomer being formed from at least one plate extending from a portion of the peripheral collar to another portion of the peripheral collar.
18. The baffle according to claim 17, wherein the at least one plate includes two plates.
19. The baffle according to claim 18, wherein the two plates extend parallel to each other.
20. The baffle according to claim 18, wherein one plate extends at an angle with respect to another plate.
21. A distillation tower comprising: a feed zone, a flash zone, a lower stripping zone located below the flash zone, a rectification zone above the flash zone, and a de-entrainment baffle located below the flash zone and above the stripping zone.
22. A distillation tower according to claim 21, wherein the baffle comprises a plurality of radial fins with openings between the fins to permit the upward passage of vapors from the portion of the tower below the baffle.
23. The distillation tower according to claim 22, wherein each fin is angularly inclined with respect to a plane passing through a central axis of the baffle such that an upper edge of the fin is displaced relative to the lower edge in the direction of flow of incoming feed to the tower.
24. The distillation tower according to claim 23, wherein each fin is angularly inclined with respect to the plane passing through the central axis of the baffle such that the upper edge of the fin is displaced relative to the lower edge in the direction of flow of incoming feed to the tower by an angle from 0° to 180°.
25. The distillation tower according to claim 24, wherein the angle is between 30° to 60°.
26. The distillation tower according to claim 24, wherein the inclination of each fin relative to the central axis of the baffle is constant along the radial length of the fin.
27. The distillation tower according to claim 22, further comprising at least one liquid downcomer to permit downward passage of liquid past the baffle.
28. The distillation tower according to claim 27, wherein the at least one liquid downcomer is located in a central portion of the baffle.
29. The distillation tower according to claim 27, wherein the at least one liquid downcomer is offset from the center of the baffle.
30. The distillation tower according to claim 27, wherein the at least one liquid downcomer comprises two spaced apart liquid passageways.
31. The distillation tower according to claim 27, wherein the at least one liquid downcomer comprises at least two downcomers, wherein one downcomer is disposed at an angle with respect to another dowcomer.
32. The distillation tower according to claim 22, wherein the baffle further comprising: a central circular hub; a peripheral collar spaced from the central circular hub, wherein the plurality of radial fins extend between the central hub and the peripheral collar.
33. The distillation tower according to claim 32, wherein the central hub comprises an open collar providing a liquid downcomer for passage of liquid downwards through the baffle.
34. The distillation tower according to claim 32, wherein the central hub comprises an upstanding circular wall member and a cover over the top of the wall member.
35. The distillation tower according to claim 32, further comprising: at least one intermediate collar spaced between the central circular hub and the periperhal collar.
36. The distillation tower according to claim 35, wherein a first set of fins extends between the central circular hub and one intermediate collar and a second set of fins extends between the intermediate collar and the peripheral collar.
37. The distillation tower according to claim 32, further comprising at least one liquid downcomer to permit downward passage of liquid past the baffle.
38. The distillation tower according to claim 37, wherein the at least one liquid downcomer being formed from at least one plate extending from a portion of the peripheral collar to another portion of the peripheral collar.
39. The distillation tower according to claim 38, wherein the at least one plate includes two plates.
40. The distillation tower according to claim 39, wherein the two plates extend parallel to each other.
41. The distillation tower according to claim 39, wherein one plate extends at an angle with respect to another plate.
42. A distillation tower according to claim 24, wherein each fin is angularly inclined with respect to a plane passing through the longitudinal axis of the tower in such a manner that the upper edge of each fin is displaced relative to the lower edge in the direction of rotational movement of the rotating vector of the incoming feed by an angle from 40° to 50°.
43. A vacuum distillation tower comprising: a stripping zone having stripping trays, a flash zone located above the stripping zone, a feed zone located above the flash zone, a feed director located in the feed zone for introducing an incoming feed into the feed zone with a rotating vector, a rectification zone above the feed zone, a radially-louvered liquid de-entrainment baffle located above the top of the stripping zone and below the feed zone, comprising a central circular hub, a peripheral collar and a plurality of radial fins extending between the central hub and the peripheral collar, with openings between the fins to permit the upward passage of vapors from the stripping zone of the tower, each fin being angularly inclined with respect to a plane passing through the longitudinal axis of the tower in such a manner that the upper edge of each fin is displaced relative to the lower edge in the direction of rotational movement of the rotating vector of the incoming feed by an angle from 30° to 60°.
Description:
CROSS REFERENCE TO RELATED APPLICATION
This application relates and claims priority to U.S. Provisional Patent Application Ser. No. 60/763,925, entitled “Distillation Tower Baffle” filed on Feb. 1, 2006, the disclosure of which is hereby incorporated specifically herein in its entirety.
FIELD OF THE INVENTION
This invention relates to a baffle for use in a distillation tower used for separating liquids into fractions of different boiling points. It is particularly applicable to vacuum distillation towers used for the fractionation of petroleum liquids but it may also be used in towers and units of other types where re-entrainment of a component separated from the incoming feed liquid presents problems, typically in atmospheric towers and fractionators in other applications.
BACKGROUND OF THE INVENTION
Separation units, such as atmospheric distillation units, vacuum distillation units and product strippers, are major processing units in a petroleum refinery or petrochemical plant. Atmospheric and vacuum distillation units are used to separate crude oil into fractions according to boiling point for downstream processing units which require feedstocks that meet particular specifications. In the initial fractionation of crude oil, higher efficiencies and lower costs are achieved if the crude oil separation is accomplished in two steps: first, the total crude oil is fractionated at essentially atmospheric pressure, and second, a bottoms stream of high boiling hydrocarbons (the atmospheric resid) is fed from the atmospheric distillation unit to a second distillation unit operating at a pressure below atmospheric, referred to as a vacuum distillation tower. The reduced pressure in the vacuum tower allows the unit to separate the bottoms fraction from the atmospheric tower into fractions at lower temperature to avoid thermally-induced cracking of the feed.
The vacuum distillation unit typically separates the bottoms stream coming from the atmospheric unit into various gas oil streams which may be categorized according to the needs of the refiner as light vacuum gas oil, heavy vacuum gas oil or vacuum distillate. The undistillable residual or bottoms fraction leaves the vacuum distillation unit as a liquid bottoms stream. Additional information concerning the use of distillation in petroleum refining is to be found in Petroleum Refining Technology and Economics, Gary, J. H. and Handwerk, G. E., pp. 31-51, Marcel Dekker, Inc. (1975), ISBN 0-8247-7150-8 as well as Modern Petroleum Technology, 4 thEd., Hobson, Applied Science Publishers, 1973, ISBN 0-8533-4487-6 and numerous other works.
In atmospheric or vacuum distillation, lighter hydrocarbons are vaporized and separated from relatively heavier hydrocarbons. Although the heavier hydrocarbons may not vaporize, they may be carried into the lighter hydrocarbons because of entrainment. This is particularly the case within many commercial designs of vacuum towers in which the two phase feed stream to the tower is generally under turbulent conditions so that the separated resid droplets are easily entrained in the vapors that are being flashed off from the incoming feed stream. Entrainment is undesirable because first, the presence of high boiling or undistillable fractions may be undesired for their physical properties, e.g. viscosity, and second, because the entrained heavier hydrocarbons are typically contaminated with metal-containing compounds such as vanadium or nickel compounds, that can poison the catalysts used in downstream processing. While some metal contaminants enter the lighter fractions by vaporization, reduction of entrainment is a more effective method of reducing metals contamination as it is the heavier fractions in which these contaminants are concentrated. For this reason, the present invention may be applied to fractionation or distillation towers regardless of the operating pressure if the construction of the towers or their operating regimes have led to re-entrainment problems; it may be applied to atmospheric towers, vacuum towers and high pressure towers or any unit in which reduction of re-entrainment is desirable.
Distillation towers often use various tangential entry devices to impart centrifugal force to the two-phase feed entering the tower. The droplets not captured in the feed zone are entrained with ascending vapors from the flash zone immediately underneath the feed zone and pass to the wash zone above the feed zone. If stripper trays are positioned at the bottom of the flash zone, the swirling feed vortex will tend to entrain resid from the top stripper tray and increase the extent of liquid entrainment, depending in part, by the shear force of the feed vapors on the liquid/froth surface of the liquid pool on the tray.
Various steps have previously been used or proposed to reduce entrainment in vacuum distillation. Demisters or wire mesh pads may be installed at some point between the flash zone and a liquid draw-off point. Demister or wire mesh pads may not, however, be completely satisfactory because they may have a tendency to plug with heavy oil and other material, have a tendency to corrode, with holes resulting from the corrosion or simply be ineffective in reducing entrainment.
Methods other than demister pads have also met with only limited success in many applications. Conventional bubble-cap trays above the flash zone may cause the vapor to pass through liquid on the bubble-cap tray, thereby allowing vapor to re-entrain liquid droplets besides creating a pressure drop which may be excessive, particularly in a vacuum tower in which the total tower pressure drop (top to bottom) should be maintained as low as is feasible.
Chimney trays having a number of risers attached to a plate having holes, with a baffle attached to the top of each riser have also been used. Chimney trays are available that use two direction changes in the flow of the vapor/liquid to improve liquid/vapor separation have a lower pressure drop than bubble-caps but they may still not be completely effective in reducing entrainment.
U.S. Pat. Nos. 4,698,138 (Silvey) and 5,972,171 (Ross) describe de-entrainment trays for vacuum towers which are based upon risers to effect improved liquid/vapor separation. Another type of de-entrainment device which has been used in various applications has taken the form of a conical baffle with vertical sides which sits over a large diameter riser located at the top of the stripper section of the vacuum tower. While this device has been effective it is relatively large and may not be suitable for installation in existing units which do not have adequate vertical clearances.
A further problem may be encountered in vacuum towers used for petroleum distillation. The bottoms stream from the atmospheric tower is passed into the flash zone of the vacuum tower where a portion of the stream is vaporized and travels up into the rectification or wash section in the upper portion of the tower. The liquid (non-vaporized) portion of the feed falls onto the trays in the stripper zone in the lower portion of the tower and may be agitated into a froth by the ascending vapor stream from the lower stripper zone as well as by the turbulent incoming feed stream; the liquid elements of the froth may then be picked up and entrained by the ascending vapors and taken up with the lighter fractions into the upper portion of the tower.
A need therefore exists to devise an improved device to reduce the degree of re-entrainment of separated liquids into the vapor stream of a distillation tower or column, particularly in vacuum and atmospheric distillation columns between the flash zone and the stripper zone. The improved device should, at the same time, cause a minimal pressure drop appropriate to use in vacuum distillation units.
SUMMARY OF THE INVENTION
The present invention provides an improved device for distillation towers or columns which effectively reduces the extent to which separated liquids are re-entrained into the vapor streams in the columns. The device is particularly suitable for use in towers which have a feed inlet located above a zone which contains liquid separated from the feed and whose entrainment is to be reduced to the extent feasible. The device is especially adapted to use in vacuum distillation towers used for fractionating petroleum atmospheric resids. In this application, it has the capability of reducing the entrainment of the liquid resid fraction into the vapor stream while, at the same time, occupying a smaller volume of the tower as compared to known types of de-entrainment device. Its simplicity of construction also makes it economical to build and install as well as providing the potential for trouble-free operation. It may be applied to towers or columns regardless of the type of feed device and so may be applied both with tangential and radial feed devices although in its preferred form described below, it is of special utility with tangential feed inlets.
According to the present invention, the distillation tower has a lower stripping zone, upper rectification zone, and a flash zone between the stripping zone and the rectification zone. An inlet for the feed to be distilled is located between the stripping zone and the rectification zone, usually within and towards the top of the flash zone. An inlet for a stripping medium, usually steam, is located in the lower part of the stripping zone so that the stripping medium passes up through the stripping zone to remove the more volatile components from the high boiling residual material which enters the stripping zone from the flash zone above it. In order to reduce the degree of re-entrainment of residual material from the stripping zone into the vapor stream ascending through the flash zone into the rectification zone, a re-entrainment reduction device is provided at the top of the stripping zone in the form of a baffle which allows the upward passage of vapor from the stripping zone but inhibits the downward flow of vapor from the flash zone into the stripping zone. This baffle may be in the form of a simple apertured plate or it may be in the form of a fabricated baffle with passages for upward vapor flow defined by upwardly directed vapor flow passages, for example, in the form of an “egg crate” baffle.
In its most preferred form, the re-entrainment reduction device takes the form of a radially-louvered baffle which is located in the portion of the tower below the feed zone. The baffle is in the form of a number of radial fins or blades, resembling a static fan with openings between the fins to permit vapors from the stripping zone in the lower portion of the tower to pass upwards through the baffle with a minimal pressure drop. The fins of the baffle are preferably oriented so that the incoming feed stream skims over the top surfaces or edges of the fins but they may be oriented at any angle with respect to the plane of the baffle, as described below.
It is an aspect of the present invention to provide a de-entrainment baffle for location in a dis
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