WO2013043195A1

WO2013043195A1 - Dividing wall column

Info

Publication number: WO2013043195A1
Application number: PCT/US2011/053082
Authority: WO
Inventors: Joe Haas; Stephen King
Original assignee: Uop Llc
Priority date: 2011-09-23
Filing date: 2011-09-23
Publication date: 2013-03-28

Abstract

Embodiments of apparatuses for fractional distillation of a feed stream are provided herein. The apparatus comprises a vessel with a dividing wall that divides a central portion of the vessel's internal volume into a first vapor-liquid contacting chamber and a second vapor-liquid contacting chamber. A first fractionation tray is disposed in the first vapor-liquid contacting chamber and comprises a first perforated horizontal decking and a first outlet downcomer that is coupled to the first perforated horizontal decking and that has a first liquid dominant section. A second fractionation tray is disposed in the second vapor-liquid contacting chamber and comprises a second perforated horizontal decking and a second outlet downcomer that is coupled to the second perforated horizontal decking. The second outlet downcomer has a second liquid dominant section that is offset with the first liquid dominant section along an axis normal to the dividing wall.

Description

DIVIDING WALL COLUMN

TECHNICAL FIELD

[0001] The present invention relates generally to apparatuses for distillation of a feed stream, and more particularly relates to apparatuses for fractional distillation of a feed stream using a vessel containing fractionation trays arranged along a dividing wall.

BACKGROUND

[0002] Fractional distillation is commonly used to separate volatile chemical mixtures in the chemical, petrochemical, and petroleum refining industries. Large scale commercial fractional distillation is conducted in an enclosed vessel referred to as a fractionation column. The fractionation column contains some form of vapor-liquid contacting device that may be in the form of packing, or alternatively, in the form of fractionation trays. A fractionation tray typically includes a large flat area referred to as the decking plus means to deliver liquid to the tray from the next tray above and to remove liquid from the tray for passage to the next tray below. The liquid being removed from the tray flows through a part of the tray referred to as an outlet downcomer. Vapor generated in the lower portion of the column passes upward through perforations in the decking while the liquid flows downward from tray to tray countercurrent to the vapor. Liquid is delivered to the tray from the outlet downcomer of the tray above and then passes across the decking contacting the vapor and exits through the outlet downcomer of the tray. The material entering the outlet downcomer is in the form of a froth or a liquid containing entrained bubbles or some form of two-phase admixture of vapor and liquid. One function of the outlet downcomer structure is to promote the separation of entrained vapor from the liquid such that only liquid passes downward to the next tray for optimum fractionation.

[0003] Conventional fractionation columns are employed to separate a feed stream into two fractions typically referred to as an overhead fraction and a bottom fraction. The overhead fraction contains the lighter or more volatile components of the feed stream and the bottom fraction contains the heavier or less volatile components. The feed stream may contain only two components that are separated in the fractionation column into two high purity streams, e.g., an overhead stream rich in the lighter component and a bottom stream rich in the heavier component. In many instances, however, the feed stream contains three or more components, e.g., a feed stream for petroleum refining may contain 100 or more different volatile components. These mixtures are typically divided by boiling point range into fractions that each contains numerous different volatile compounds. To separate such a feed stream into three product streams, two conventional fractionation columns fluidly coupled in series can be employed. The first fractionation column forms a first product stream rich in either the lighter or heavier volatile component(s) and a second product stream rich in the remaining components. The second product stream is then passed into a second fractionation column to separate the second product stream into two other product streams, one rich in the intermediate volatile component(s) and the other rich in either the heavier or lighter volatile component(s).

[0004] In some instances, these two column arrangements can be integrated into a single column that contains a dividing wall ("dividing wall column") to reduce operating and capital costs. The dividing wall divides an internal volume of the column into two open ended, parallel vapor-liquid contacting chambers to facilitate separating the intermediate boiling fraction from the lighter and heavier components to produce a side stream that contains the intermediate fraction in addition to producing the overhead and bottom streams. Unfortunately, the use of dividing wall columns to separate a feed stream is limited because these columns need to operate with relatively little temperature difference between the two open ended-parallel vapor-liquid contacting chambers to minimize heat transfer through the dividing wall. In particular, heat transferred through the dividing wall can cause undesirable reboiling in the outlet downcomer(s). That is, the liquid in the downcomer is close to its boiling point and any small input of heat via the dividing wall into the liquid can cause the formation of reboiled vapor. The reboiled vapor is expanded and rises through the downcomer countercurrent to the liquid flow, possibly choking the liquid flow through the downcomer and detracting from the overall separation.

[0005] Accordingly, it is desirable to provide apparatuses for fractional distillation of a feed stream comprising a dividing wall column that can operate with an increased temperature difference between the vapor-liquid contacting chambers without choking the liquid flow through the downcomer(s) and detracting from the overall separation of the feed stream. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. BRIEF SUMMARY

[0006] Apparatuses for fractional distillation of a feed stream are provided herein. In accordance with an exemplary embodiment, an apparatus for fractional distillation of a feed stream is provided. The apparatus comprises a vessel comprising a cylindrical wall that extends vertically and that encloses an internal cylindrical volume having a central portion. A dividing wall extends vertically through the central portion to divide the central portion into a first vapor-liquid contacting chamber and a second vapor-liquid contacting chamber. A plurality of fractionation trays includes a first fractionation tray and a second fractionation tray. The first fractionation tray is disposed in the first vapor-liquid contacting chamber vertically spaced between a lower first additional fractionation tray and an upper first additional fractionation tray. The first fractionation tray comprises a first perforated horizontal decking and a first outlet downcomer that is coupled to the first perforated horizontal decking and that has a first liquid dominant section. The first perforated horizontal decking is configured to carry a first vapor-liquid froth that comprises a first vapor fraction and a first liquid fraction. The first outlet downcomer is configured to remove a first portion of the first vapor-liquid froth from the first perforated horizontal decking, to release the first vapor fraction from the first portion to form a first vapor-phase volume that is disposed between a remaining portion of the first vapor-liquid froth and the upper first additional fractionation tray, and to advance the first liquid fraction from the first portion through the first liquid dominant section to the lower first additional fractionation tray. The second fractionation tray is disposed in the second vapor-liquid contacting chamber and comprises a second perforated horizontal decking and a second outlet downcomer that is coupled to the second perforated horizontal decking and that has a second liquid dominant section. The second perforated horizontal decking is configured to carry a second vapor-liquid froth that comprises a second vapor fraction and a second liquid fraction. The second outlet downcomer is configured to remove a second portion of the second vapor-liquid froth from the second perforated horizontal decking, to release the second vapor fraction from the second portion, and to advance the second liquid fraction from the second portion through the second liquid dominant section to a lower second additional fractionation tray. The second liquid dominant section is aligned with the remaining portion of the first vapor-liquid froth, the first vapor-phase volume, or a combination thereof along an axis normal to the dividing wall. An inlet is for introducing the feed stream to the vessel. The apparatus is configured to separate the feed stream using the plurality of fractionation trays into a heavy-ends product stream, an intermediate-ends product stream, and a light-ends product stream. A lower outlet, a side outlet, and an upper outlet are for removing the heavy-ends product stream, the intermediate-ends product stream, and the light-ends product stream, respectively, from the vessel.

[0007] In accordance with another exemplary embodiment, an apparatus for fractional distillation of a feed stream is provided. The apparatus comprises a vessel comprising a cylindrical wall that extends vertically and that encloses an internal cylindrical volume having a central portion. A dividing wall extends vertically through the central portion to divide the central portion into a first vapor-liquid contacting chamber and a second vapor- liquid contacting chamber. A plurality of fractionation trays includes a first fractionation tray, a second fractionation tray, and a third fractionation tray. The first fractionation tray and the second fractionation tray are disposed in the first vapor-liquid contacting chamber. The first fractionation tray is positioned at a first contacting elevation and the second fractionation tray is positioned above the first fractionation tray at a second contacting elevation. The first fractionation tray comprises a first outlet downcomer that has a first liquid dominant section and the second fractionation tray comprises a second outlet downcomer that has a second liquid dominant section. The first outlet downcomer is configured to remove a first liquid fraction from the first fractionation tray including advancing the first liquid fraction through the first liquid dominant section to a lower first additional fractionation tray. The second outlet downcomer is configured to remove a second liquid fraction from the second fractionation tray including advancing the second liquid fraction through the second liquid dominant section to the first fractionation tray. The third fractionation tray is disposed in the second vapor-liquid contacting chamber and is positioned at a third contacting elevation that is between the first and second contacting elevations. The third fractionation tray comprises a third outlet downcomer that has a third liquid dominant section. The third outlet downcomer is configured to remove a third liquid fraction from the third fractionation tray including advancing the third liquid fraction through the third liquid dominant section to a lower second additional fractionation tray. The third liquid dominant section is offset with the first and second liquid dominant sections along an axis normal to the dividing wall to mitigate heat transfer through the dividing wall. An inlet is for introducing the feed stream to the vessel. The apparatus is configured to separate the feed stream using the plurality of fractionation trays into a heavy-ends product stream, an intermediate-ends product stream, and a light-ends product stream. A lower outlet, a side outlet, and an upper outlet are for removing the heavy-ends product stream, the intermediate-ends product stream, and the light-ends product stream, respectively, from the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:

[0009] FIG. 1 schematically illustrates an apparatus for fractional distillation of a feed stream in accordance with an exemplary embodiment;

[0010] FIG. 2A is a sectional view of the apparatus depicted in FIG. 1 along line 2-2 in accordance with one embodiment;

[0011] FIG. 2B is a sectional view of the apparatus depicted in FIG. 1 along line 2-2 in accordance with another embodiment;

[0012] FIG. 3 is a sectional view of the apparatus depicted in FIG. 2A along line 3-3;

[0013] FIG. 4 is a sectional view of the apparatus depicted in FIG. 1 along line 4-4;

[0014] FIG. 5A is a sectional view of the apparatus depicted in FIG. 4 along line 5A-5A;

[0015] FIG. 5B is a sectional view of the apparatus depicted in FIG. 4 along line 5B-5B;

[0016] FIG. 5C is a sectional view of the apparatus depicted in FIG. 4 along line 5C-5C;

[0017] FIG. 6A is a sectional view of the apparatus depicted in FIG. 1 along line 6-6 in accordance with one embodiment; and

[0018] FIG. 6B is a sectional view of the apparatus depicted in FIG. 1 along line 6-6 in accordance with another embodiment. DETAILED DESCRIPTION

[0019] The following Detailed Description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

[0020] Various embodiments contemplated herein relate to apparatuses for fractional distillation of a feed stream. The exemplary embodiments taught herein provide an apparatus comprising a vessel and a dividing wall that extends through a central portion of an internal volume of the vessel to divide the central portion into a first vapor-liquid contacting chamber and a second vapor-liquid contacting chamber. A plurality of fractionation trays are arranged in the vessel including a first fractionation tray that is disposed in the first vapor-liquid contacting chamber and a second fractionation tray that is disposed in the second vapor-liquid contacting chamber. The first and second

fractionation trays are disposed along opposing sides of the dividing wall preferably just about laterally adjacent to each other but at offset elevations. The first fractionation tray is vertically spaced between a lower fractionation tray and an upper fractionation tray. The first fractionation tray comprises a first perforated horizontal decking and a first outlet downcomer that is coupled to the first perforated horizontal decking. The first perforated horizontal decking carries a vapor-liquid froth that comprises a vapor fraction and a liquid fraction. The first outlet downcomer removes a portion of the vapor-liquid froth from the first perforated horizontal decking, releasing the vapor fraction from the removed portion to form a vapor-phase volume that is disposed above the first fractionation tray between a remaining portion of the vapor-liquid froth and the upper fractionation tray. The liquid fraction from the removed portion of vapor-liquid froth is now substantially free of any entrained vapor from the vapor fraction and is advanced through a first liquid dominant section of the first outlet downcomer to the lower fractionation tray.

[0021] The second fractionation tray comprises a second perforated horizontal decking and a second outlet downcomer that is coupled to the second perforated horizontal decking. The second perforated horizontal decking carries a vapor-liquid froth that comprises a vapor fraction and a liquid fraction. The second outlet downcomer removes a portion of the vapor-liquid froth from the second perforated horizontal decking, releasing the vapor fraction from the removed portion. The liquid fraction from the removed portion of vapor-liquid froth is now substantially free of any entrained vapor from the vapor fraction and is advanced through a second liquid dominant section of the second outlet downcomer to a lower additional fractionation tray. In an exemplary embodiment, the second liquid dominant section of the second fractionation tray does not align with the first liquid dominant section of the first fractionation tray normal to the dividing wall.

Rather, the second liquid dominant section preferably aligns with the remaining portion of the vapor-liquid froth and/or the vapor-phase volume associated with the first fractionation tray such that an axis is defined by the alignment that is normal to the dividing wall. With such an arrangement, the inventors have found that less heat is transferred through the dividing wall to the liquid fractions passing through the first and second liquid dominant sections compared with conventional processes even with relatively higher temperature differences between the first and second vapor-liquid contacting chambers that would otherwise cause choking in the first and/or second outlet downcomers. In particular, the liquid dominant sections of the downcomers contain the liquid fractions from the corresponding vapor-liquid froths essentially without any entrained vapor. The liquid fractions are more thermally conductive than the vapor fractions and therefore, the vapor fractions act essentially as insulators, conducting or transferring substantially less heat than the liquid fractions. By positioning the second liquid dominant section, which contains primarily the liquid fraction, against the dividing wall aligned with and directly opposite the vapor-phase volume and/or the remaining portion of the vapor-liquid froth (both of which contain a significant amount of the vapor fraction) associated with first fractionation tray, less heat will transfer through the dividing wall to the first and/or second outlet downcomers because the vapor fraction acts more like an insulator, conducting or transferring less heat to or from the dividing wall.

[0022] Referring to FIG. 1, a schematic depiction of an apparatus 10 for fractional distillation of a multi-component feed in accordance with an exemplary embodiment is provided. The apparatus 10 includes a vessel 12 that has a cylindrical wall 14 that extends vertically and encloses an internal cylindrical volume 16. As illustrated, the apparatus 10 is configured as a dividing wall fractionation column and has a dividing wall 18 that extends vertically through a central portion 20 of the internal cylindrical volume 16. The dividing wall 18 divides the central portion 20 into a feed vapor-liquid contacting chamber 22 and a product vapor-liquid contacting chamber 24.

[0023] A feed stream 26 is introduced to the vessel 12. In an exemplary embodiment, the feed stream 26 is a multi-component mixture containing light-end components, intermediate-end components, and heavy-end components. For example, the feed stream 26 may be a petroleum refining stream that contains hydrotreated naphtha including light naphtha as the light-end components, e.g., C₅-, heartcut naphtha as the intermediate-end components, e.g., Ce - Cio, and heavy naphtha as the heavy-end components, Cn+. As used herein, C_x means hydrocarbon molecules that have "X" number of carbon atoms, C_x+ means hydrocarbon molecules that have "X" and/or more than "X" number of carbon atoms, and C_x- means hydrocarbon molecules that have "X" and/or less than "X" number of carbon atoms. Alternatively, the feed stream 26 may be any other multi-component mixture that contains three or more volatile components.

[0024] The feed stream 26 enters the vessel 12 and is separated in the feed vapor-liquid contacting chamber 22 via fractional distillation using a plurality of feed chamber fractionation trays 28 that are arranged along the dividing wall 18 as will be discussed in further detail below. The feed stream 26 is divided into less volatile components, e.g., the heavy naphtha and some of the heartcut naphtha, that descend downward in a liquid phase and more volatile components, e.g., the light naphtha and some of the heartcut naphtha, that ascend upward in a vapor phase. Both the upper and lower ends of the feed and product vapor-liquid contacting chambers 22 and 24 are open and therefore, the vapor phase may pass upward out of the feed vapor-liquid contacting chamber 22 into an upper portion 30 of the vessel 12.

[0025] Referring also to FIGS. 2A and 3, the upper portion 30 of the vessel 12 contains a plurality of full diameter fractionation trays 32 for fractional distillation of the vapor phase. The full diameter fractionation trays 32 each comprise a perforated horizontal decking 42 that carries a vapor-liquid froth 48 and that defines an elevation or level 31 of the tray. In general and as is well known in fractional distillation, the froth carried across a particular fractionation tray will have a distinct composition corresponding to the relative volatility of the components contained in the froth and the vapor-liquid equilibrium of those components at the particular temperature and pressure about the tray. As illustrated, the full diameter fractionation trays 32 are configured as single-pass cross flow trays 33, which means that the vapor-liquid froth 48 passes from an inlet side 34 to an outlet side 36 of the perforated horizontal decking 42 in a single direction indicated by arrow 47 before entering an outlet downcomer 38 and flowing onto the next lower tray. Alternatively and as illustrated in FIG. 2B, one or more of the full diameter fractionation trays 32 may be configured as a double pass tray 35 having two inlet sides 34 disposed on opposing end portions of the full diameter tray fractionation 32 and the outlet downcomer 38 that is formed in a center portion of the full diameter fractionation tray 32 such that the vapor-liquid froth 48 flows from the inlet sides 34 inwardly in two opposing directions indicated by arrows 37 towards the outlet downcomer 38. [0026] Referring back to FIGS. 2A and 3, the outlet downcomer 38 includes a downcomer end wall 40 that extends above the perforated horizontal decking 42 to form an outlet weir 44 for removing a portion of the vapor-liquid froth 48 from the perforated horizontal decking 42. The downcomer end wall 40 extends below the perforated horizontal decking 42 to form an outlet apron 46 that confines a downcomer volume to allow vapor entrained in the vapor-liquid froth 48 to escape, leaving essentially only a liquid fraction 50 in a liquid dominant section 52 of the outlet downcomer 38. The bottom edge of the downcomer end wall 40 is a short distance from the level 31 of the next lower tray to allow the liquid fraction 50 to flow through and onto the next lower tray.

[0027] Referring back to FIG. 1, a portion of the liquid collected from the lowermost full diameter fractionation tray 32 in the upper portion 30 of the vessel 12 is preferably rich in intermediate-end components and is fed to the top of the product vapor-liquid contacting chamber 24. A second portion of the liquid collected from the lowermost full diameter fractionation tray 32 in the upper portion 30 is fed to the top of the feed vapor- liquid contacting chamber 22. As illustrated, an overhead vapor stream 54 that is preferably rich in the light-end components is removed from the top of the vessel 12 and is passed through a condenser 56 to form an overhead liquid 57. The overhead liquid 57 is collected in an overhead receiver 58. The overhead liquid 57 is removed from the overhead receiver 58 and divided into a first portion 60 as a net overhead product and a second portion 62 that is returned to the vessel 12 as reflux.

[0028] In a manner analogous to the upper portion 30 of the vessel 12, the liquid phase separated from the feed stream 26 passes downward out of the feed vapor-liquid contacting chamber 22 into a lower portion 64 of the vessel 12. The lower portion 64 contains a plurality of the full diameter fractionation trays 32 configured as discussed above. The liquid phase is subject to fractional distillation on these full diameter fractionation trays 32 leading to the formation of a liquid stream 66 that is preferably rich in the heavy-end components. The liquid stream 66 is removed from the bottom of the vessel 12 and is divided into a first portion 68 as a net bottom product and a second portion 70. The second portion 70 is passed through a reboiler 72 to form a heated second portion 74 that is returned to the lower portion 64 of the vessel 12. The heat added to the lower portion 64 by the heated second portion 74 forms a vapor that passes upward through the perforations in the full diameter fractionation trays 32 and enters the bottoms of the feed and product vapor-liquid contacting chambers 22 and 24 on both sides of the dividing wall 18. Accordingly, vapor enters the bottoms of the feed and product vapor- liquid contacting chambers 22 and 24 and liquid enters the tops of the feed and product vapor-liquid contacting chambers 22 and 24, generating a countercurrent flow necessary for fractional distillation in the two chambers 22 and 24. In the product vapor-liquid contacting chamber 24, a plurality of product chamber fractionation trays 76 that are arranged along the dividing wall 18. The portions of the liquid and vapor entering the product vapor- liquid contacting chamber 24 are subject to fractional distillation using the product chamber fractionation trays 76 to form an intermediate stream 75 that is preferably rich in the intermediate-end components.

[0029] Referring also to FIG. 4, the feed and product chamber fractionation trays 28 and 76 are configured similar to the full diameter fractionation trays 32 as discussed above except they are smaller in area and have a chordal shape. The chordal shape of the feed and product chamber fractionation trays 28 and 76 includes a cord defined by the dividing wall 18, which can be positioned off-center in the vessel 12 such that the area of either the feed or product chamber fractionation trays 28 or 76 can be greater than the other.

[0030] As illustrated in FIG. 1, the product chamber fractionation trays 76 are preferably at elevations or levels 31 that are offset from the corresponding levels 31 of the feed chamber fractionation trays 28. In an exemplary embodiment, the vertical spacing indicated by double-headed arrow 43 between vertically adjacent feed chamber fractionation trays 28 is about 400 to about 800 mm, and the vertical spacing indicated by double-headed arrow 45 between vertically adjacent product chamber fractionation trays 76 is about 400 to about 800 mm. In another exemplary embodiment, the product chamber fractionation trays 76 are at levels 31 that are offset from the corresponding levels 31 of the feed chamber fractionation trays by a vertical distance indicated by double headed arrow 49 of about 150 to about 400 mm, and preferably of about 200 to about 350 mm.

[0031] Referring to FIGS. 4-5B, each of the feed chamber fractionation trays 28 are formed from two major components, a perforated horizontal decking 142 and an outlet downcomer 138 that includes a downcomer wall 140 coupled to the perforated horizontal decking 142. Similarly, each of the product chamber fractionation trays 76 are formed from two major components, a perforated horizontal decking 242 and an outlet downcomer 238 that includes a downcomer wall 240 coupled to the perforated horizontal decking 242. As illustrated, the feed and product chamber fractionation trays 28 and 76 are configured as single-pass cross flow trays 33. In particular, a vapor-liquid froth 148 passes from an inlet side 134 to an outlet side 136 of the perforated horizontal decking 142 in a single direction indicated by the arrow 147 before entering the outlet downcomer 138 and flowing onto the next lower tray, and a vapor-liquid froth 248 passes from an inlet side 234 to an outlet side 236 of the perforated horizontal decking 242 in a single direction indicated by arrow 247 before entering the outlet downcomer 238 and flowing onto the next lower tray. The outlet downcomers 138 preferably alternate from side to side along the cylindrical wall 14 for vertically adjacent feed chamber fractionation trays 28, and the outlet downcomers 238 preferably alternate side to side along the cylindrical wall 14, opposite the outlet downcomers 138, for vertically adjacent product chamber fractionation trays 76. As such, the vapor-liquid froth 148 passes in a direction that is countercurrent to the direction of the vapor-liquid froth 248 for neighboring feed and product chamber fractionation trays 28 and 76. Alternatively, one or more of the feed and/or product chamber fractionation trays 28 and 76 may be configured as a double pass tray 35, a combination of double pass trays 35, a single-pass cross flow tray on one side of the dividing wall 18 and a double pass tray on the other side of the dividing wall 18 (e.g. see FIGS 6A and/or 6B), fractionation tray(s) with three or four passes depending on the tray capacity demand, proprietary specialty trays, and/or any other fractionation tray(s) known to those skilled in the art.

[0032] As the vapor-liquid froths 148 and 248 flow through their respective outlet downcomers 138 and 238, vapor entrained in the vapor-liquid froths 148 and 248 escapes, leaving essentially only the liquid fractions 150 and 250 correspondingly in the liquid dominant sections 152 and 252 of the lower portions of the outlet downcomers 138 and

238. The escaped vapor form vapor-phase volumes 153 and 253 correspondingly between the vapor-liquid froths 148 and 248 flowing along the feed and product chamber fractionation trays 28 and 76 and the next trays above. The liquid fractions 150 and 250 flow through the liquid dominant sections 152 and 252, respectively, onto the next lower trays.

[0033] Referring to FIG. 5C, a sectional view, facing normal to the dividing wall 18, of the feed vapor-liquid contacting chamber 22 including multiple levels of the feed chamber fractionation trays 28 is provided. In an exemplary embodiment, the liquid dominant sections 252, indicated in dashed lines, of the product chamber fractionation trays 76 do not align with the liquid dominant sections 152 of the feed chamber fractionation trays 28 as viewed normal to the dividing wall 18. Preferably, the feed chamber fractionation trays 28 and product chamber fractionation trays 76 are staggered or at offset elevations or levels 31 relative to each other (see FIGS. 5A-5B) and the liquid dominant sections 152 alternate along opposite end portions of the dividing wall 18 at vertically adjacent levels 31, opposite the liquid dominant sections 252 that alternate on the opposite side of the dividing wall 18 along opposite end portions of the dividing wall 18 at vertically adjacent levels 31, such that the liquid dominant sections 252 do not align with the liquid dominant sections 152 as viewed normal to the dividing wall 18. In another exemplary embodiment, as viewed normal to the dividing wall 18, the liquid dominant sections 252 align with the vapor-liquid froth 148 flowing on the feed chamber fractionation trays 28 and/or with the vapor-phase volumes 153, and preferably with the vapor-phase volumes 153, and the liquid dominant sections 152 align with the vapor-liquid froths 248 flowing on the product chamber fractionation trays 76 and/or with the vapor-phase volumes 253, and preferably with the vapor-phase volumes 253. As discussed above, the liquid fractions 150 and 250 are more thermally conductive than the vapor fractions contained in the vapor-liquid froths 148 and 248 and in the vapor-phase volumes 153 and 253. By positioning the liquid dominant sections 152 and 252 against the dividing wall 18 aligned with and directly opposite the vapor-liquid froths 148 and 248 and/or the vapor-phase volumes 153 and 253, less heat is transferred through the dividing wall to or from the liquid fractions flowing through the outlet downcomers 138 and 238. With this arrangement, the liquid dominant sections will not be adjacent to each other on opposite sides of the dividing wall 18.

Moreover, by having the feed chamber fractionation trays 28 and product chamber fractionation trays 76 at offset elevations or levels 31 relative to each other, the vapor- liquid froths 148 and 248, which are moderately thermally conductive because they also contain some of the more thermally conductive liquid fractions, are offset relative to each other and are preferably aligned with the vapor-phase volumes 253 and 153, respectively, to further mitigate heat transfer through the dividing wall 18. The apparatus 10 can preferably be operated with a temperature difference between the feed chamber fractionation trays 28 and the product chamber fractionation trays 76 at neighboring levels 31 of about 15°C or greater and preferably of from about 20 to about 45°C.

[0034] Accordingly, apparatuses for fractional distillation of a feed stream have been described. The apparatus is configured as a dividing wall column with a plurality of fractionation trays arranged along two opposing sides of a dividing wall in which the liquid dominant sections of the fractionation trays do not align with each other as viewed normal to the dividing wall. With such an arrangement, less heat is transferred through the dividing wall to the liquid fractions passing through the liquid dominant sections compared with conventional processes even with relatively higher temperature differences between laterally neighboring fractionation trays that might otherwise detract from the overall separation of the feed stream.

[0035] While at least one exemplary embodiment has been presented in the foregoing Detailed Description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing Detailed Description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended Claims and their legal equivalents.

Claims

CLAIMS What is claimed is:

1. An apparatus for fractional distillation of a feed stream, the apparatus comprising:

a vessel comprising a cylindrical wall that extends vertically and that encloses an internal cylindrical volume having a central portion;

a dividing wall extending vertically through the central portion to divide the central portion into a first vapor-liquid contacting chamber and a second vapor- liquid contacting chamber;

a plurality of fractionation trays including:

a first fractionation tray disposed in the first vapor-liquid contacting chamber vertically spaced between a lower first additional fractionation tray and an upper first additional fractionation tray, wherein the first fractionation tray comprises a first perforated horizontal decking and a first outlet downcomer that is coupled to the first perforated horizontal decking and that has a first liquid dominant section, wherein the first perforated horizontal decking is configured to carry a first vapor-liquid froth that comprises a first vapor fraction and a first liquid fraction, and the first outlet downcomer is configured to remove a first portion of the first vapor-liquid froth from the first perforated horizontal decking, to release the first vapor fraction from the first portion to form a first vapor-phase volume that is disposed between a remaining portion of the first vapor-liquid froth and the upper first additional fractionation tray, and to advance the first liquid fraction from the first portion through the first liquid dominant section to the lower first additional fractionation tray; and

a second fractionation tray disposed in the second vapor-liquid contacting chamber and comprising a second perforated horizontal decking and a second outlet downcomer that is coupled to the second perforated horizontal decking and that has a second liquid dominant section, wherein the second perforated horizontal decking is configured to carry a second vapor-liquid froth that comprises a second vapor fraction and a second liquid fraction, and the second outlet downcomer is configured to remove a second portion of the second vapor- liquid froth from the second perforated horizontal decking, to release the second vapor fraction from the second portion, and to advance the second liquid fraction from the second portion through the second liquid dominant section to a lower second additional fractionation tray, and wherein the second liquid dominant section is aligned with the remaining portion of the first vapor-liquid froth, the first vapor-phase volume, or a combination thereof along an axis normal to the dividing wall;

an inlet for introducing the feed stream to the vessel, wherein the apparatus is configured to separate the feed stream using the plurality of fractionation trays into a heavy-ends product stream, an intermediate-ends product stream, and a light- ends product stream; and

a lower outlet, a side outlet, and an upper outlet for removing the heavy- ends product stream, the intermediate-ends product stream, and the light-ends product stream, respectively, from the vessel.

2. The apparatus according to claim 1, wherein the first perforated horizontal decking is at a first contacting elevation and the second perforated horizontal decking is at a second contacting elevation that is offset from the first contacting elevation.

3. The apparatus according to claim 2, wherein the second contacting elevation is offset from the first contacting elevation by a vertical distance of from about 150 to about 450 mm.

4. The apparatus according to claim 2, wherein the second contacting elevation is offset from the first contacting elevation by a vertical distance of from about 200 to about 350 mm.

5. The apparatus according to claim 1, wherein the second liquid dominant section does not align with the first liquid dominant section along the axis normal to the dividing wall.

6. The apparatus according to claim 1, wherein the first fractionation tray and the second fractionation tray are configured such that the first vapor-liquid froth is carried across the first perforated horizontal decking in a first direction and the second vapor-liquid froth is carried across the second perforated horizontal decking in a second direction that is countercurrent to the first direction.

7. The apparatus according to claim 1, wherein the first and second fractionation trays are configured as single pass cross flow fractionation trays.

8. The apparatus according to claim 7, wherein the first outlet downcomer is disposed along a first side and a first end portion of the dividing wall and the second outlet downcomer is disposed along a second side and a second end portion of the dividing wall disposed opposite from the first side and the first end portion.

9. The apparatus according to claim 1, wherein the first fractionation tray, the second fractionation tray, or a combination thereof is configured as a double pass tray or a combination of double pass trays.

10. The apparatus according to claim 1, wherein the apparatus is configured to operate with a temperature difference between the first and second fractionation trays of about 15°C or greater without choking the first outlet downcomer with the first vapor-liquid froth or the second outlet downcomer with the second vapor- liquid froth.

1 1. The apparatus according to claim 1, wherein the apparatus is configured to operate with a temperature difference between the first and second fractionation trays of from about 20 to about 45°C without choking the first outlet downcomer with the first vapor-liquid froth or the second outlet downcomer with the second vapor-liquid froth.

12. The apparatus according to claim 1, wherein the first and second fractionation trays are configured such that the second liquid dominant section is aligned with the first vapor-phase volume along the axis normal to the dividing wall.

13. The apparatus according to claim 1, wherein the first and second vapor-liquid froths are offset to each other along the axis normal to the dividing wall to mitigate heat transfer through the dividing wall.

14. An apparatus for fractional distillation of a feed stream, the apparatus comprising:

a plurality of fractionation trays including:

a first fractionation tray and a second fractionation tray that are disposed in the first vapor-liquid contacting chamber, wherein the first fractionation tray is positioned at a first contacting elevation and the second fractionation tray is positioned above the first fractionation tray at a second contacting elevation, wherein the first fractionation tray comprises a first outlet downcomer that has a first liquid dominant section and the second fractionation tray comprises a second outlet downcomer that has a second liquid dominant section, and wherein the first outlet downcomer is configured to remove a first liquid fraction from the first fractionation tray including advancing the first liquid fraction through the first liquid dominant section to a lower first additional fractionation tray, and the second outlet downcomer is configured to remove a second liquid fraction from the second fractionation tray including advancing the second liquid fraction through the second liquid dominant section to the first fractionation tray; and

a third fractionation tray disposed in the second vapor-liquid contacting chamber and positioned at a third contacting elevation that is between the first and second contacting elevations, wherein the third fractionation tray comprises a third outlet downcomer that has a third liquid dominant section, wherein the third outlet downcomer is configured to remove a third liquid fraction from the third fractionation tray including advancing the third liquid fraction through the third liquid dominant section to a lower second additional fractionation tray, and wherein the third liquid dominant section is offset with the first and second liquid dominant sections along an axis normal to the dividing wall to mitigate heat transfer through the dividing wall;

15. The apparatus according to claim 14, wherein the first outlet downcomer is disposed along a first side and a first end portion of the dividing wall and the second outlet downcomer is disposed along a second side and a second end portion of the dividing wall disposed opposite from the first side and the first end portion.

16. The apparatus according to claim 14, wherein a first vertical distance defined from the first contacting elevation to the second contacting elevation is from about 400 to about 800 mm.

17. The apparatus according to claim 14, wherein a second vertical distance defined from the first contacting elevation to the third contacting elevation is from about 150 to about 450 mm.

18. The apparatus according to claim 14, wherein a third vertical distance defined from the second contacting elevation to the third contacting elevation is from about 150 to about 450 mm.

19. The apparatus according to claim 14, wherein the first and second fractionation trays are configured as single pass cross flow fractionation trays, and the first and second outlet downcomers are disposed along opposing end portions of one side of the dividing wall.

20. The apparatus according to claim 14, wherein the apparatus is configured to operate with a temperature difference between the third fractionation tray and the first fractionation tray or the second fractionation tray of about 15°C or greater.